题目内容
（请给出正确答案）
For a linear continuous-time system, when the initial state is
and the input signal is
, the output is
,
; when the initial state is
and the input signal is, the output is
,
. Then, what is the output when the initial state isand the input signal is
？ ()
A、
B、
,
C、
,
D、
,
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第1题
For a C-T LTI system, the input
and the impulse response of the system
are shown below. Then the value of the zero-state response of the system
at
is ( ).
A、-2
B、-1
C、0
D、1
第2题
A uni feedback system, the process is
The system is controlled by a proportional controller
,
The value of K that yields a steady-state error
witha magnitude equal to 0.01 for a unit step input is:
A、K = 49
B、K=99
C、K=169
D、None of the above
第3题
??A welfare client is supposed to cheat. Everybody expects it. Faced with sharing a dinner of raw pet food with the cat, many people in wheelchairs I know bleed the system for a few extra dollars. They tell the government that they are getting two hundred dollars less than their real pension so they can get a little extra welfare money. Or, they tell the caseworker that the landlord raised the rent by a hundred dollars.
??I have opted to live a life of complete honesty. So instead, I go out and drum up some business and draw cartoons. I even tell welfare how much I make! Oh, I'm tempted to get paid under the table. But even if I yielded to that temptation, big magazines are not going to get involved in some sticky situation. They keep my records, and that information goes right into the government's computer. Very high-profile.
??As a welfare client I'm expected to bow before the caseworker. Deep down, caseworkers know that they are being made fools of by many of their clients, and they feel they are entitled to have clients bow to them as compensation. I'm not being bitter. Most caseworkers begin as college-educated liberals with high ideals. But after a few years in a system that practically requires people to lie, they become like the one I shall call "Suzanne", a detective in shorts.
??Not long after Christmas last year, Suzanne came to inspect my apartment and saw some new posters pasted on the wall. "Where'd you get the money for those？" she wanted to know.
??"Friends and family."
??"Well, you'd better have a receipt for it, by God. You have to report any donations or gifts."
??This was my cue to beg. Instead, I talked back. "I got a cigarette from somebody on the street the other day. Do I have to report that？"
??"Well, I'm sorry, but I don't make the rules, Mr. Callahan."
??Suzanne tries to lecture me about repairs to my wheelchair, which is always breaking down because welfare won't spend money maintaining it properly. "You know, Mr. Callahan, I've heard that you put a lot more miles on that wheelchair than average."
??Of course I do. I'm an active worker, not a vegetable. I live near downtown, so I can get around in a wheelchair. I wonder what she'd think if she suddenly broke her hip and had to crawl to work.
??Government cuts in welfare have resulted in hunger and suffering for a lot of people, not just me. But people with spinal cord injuries felt the cuts in a unique way: The government stopped taking care of our chairs. Each time mine broke down, lost a screw, needed a new roller bearing, the brake wouldn't work, etc., and I called Suzanne, I had to endure a little lecture. Finally, she'd say, "Well, if I can find time today, I'll call the medical worker."
??She was supposed to notify the medical worker, who would certify that there was a problem. Then the medical worker called the wheelchair repair companies to get the cheapest bid. Then the medical worker alerted the main welfare office at the state capital. They considered the matter for days while I lay in bed, unable to move. Finally, if I was lucky, they called back and approved the repair.
??When welfare learned I was making money on my cartoons, Suzanne started "visiting" every fortnight instead of every two months. She looked into every comer in search of unreported appliances, or maids, or a roast pig in the oven, or a new helicopter parked out back. She never found anything, but there was always a thick pile of forms to fill out at the end of each visit, accounting for every penny.
??There is no provision in the law for a gradual shift away from welfare. I am an independent businessman, slowly building up my market. It's impossible to jump off welfare and suddenly be making two thousand dollars a month. But I would love to be able to pay for some of my living and not have to go through an embarrassing situation every time I need a spare part for my wheelchair.
??There needs to be a lawyer who can act as a champion for the rights of welfare clients, because the system so easily lends itself to abuse by the welfare givers as well as by the clients. Welfare sent Suzanne to look around in my apartment the other day because the chemist said I was using a larger than usual amount of medical supplies. I was, indeed: The hole that has been surgically cut to drain urine had changed size and the connection to my urine bag was leaking.
??While she was taking notes, my phone rang and Suzanne answered it. The caller was a state senator, which scared Suzanne a little. Would I sit on the governor's committee and try to do something about the thousands of welfare clients who, like me, could earn part or all of their own livings if they were allowed to do so, one step at a time？
Hell, yes, I would! Someday people like me will thrive under a new system that will encourage them, not seek to convict them of cheating. They will be free to develop their talents without guilt or fear--or just hold a good, steady job.
第4题
第5题
called Kinshasa, shortly before the waves of violent rebellion that followed the liberation of the Belgian Congo.A seemingly healthy man walked into a hospital clinic to give blood for a Western-backed study of blood diseases.He walked away and was never heard from again.Doctors analyzed his sample, froze it in a lest tube and forgot about it.A quarter-century later, in the mid-1980s, researchers studying the growing AIDS epidemic took a second look at the blood and discovered that it contained HIV, the virus that causes AIDS.
And not just any HIV.The Leopoldville sample is the oldest specimen of the AIDS virus ever isolated and may now help solve the mystery of how and when the virus made the leap from animals(monkeys or chimpanzees)to humans, according to a report published last week in Nature.Dr.David Ho, director of the Aaron Diamond AIDS Research Center in New York City and one of the study’s authors, says a careful genetic analysis of sample’s DNA pushes the putative origin of the AIDS epidemic back at least a decade, to the early 1950s or even the 1940s.
Over the past 15 years, scientists have identified at least 10 subtypes of the AIDS virus.But they couldn’t tell whether they were seeing variations on one changeable virus or the handiwork of several different viruses that had made the jump from primates to man.A close look at the genetic mutations in the Leopoldville sample strongly suggests that all it look to launch the AIDS epidemic was one unlucky turn of events.
By comparing the DNA of the 1959 virus with that of samples taken from the 1980s and 1990s , Ho and his colleagues constructed a viral family tree in which the Leopoldville isolate sits right at the juncture where three subtypes branch out.The 39-year-old specimen is also strikingly similar to the other seven subtypes.The clear implication: all the viral strains can be traced back to a single event or a closely related group of events.One theory is that AIDS started through contact with infected monkeys in a remote area and spread to the rest of the population through urbanization and mass inoculations.
The findings underscore how rapidly HIV can adapt to its surroundings, making it devilishly difficult to develop effective vaccines.No one knows how many more subtypes of HIV will sprout in the next 40 years, but chances are that they will be every bit as lethal as the ones we see today, if not more so.
36.What does the phrase “Belgian Congo” mean?
A.Belgium was a colony of Congo.
B.Congo was a colony of Belgium.
C.Belgian Congo was a African state.
D.Belgium and Congo were two separate countries.
37.According to this article, HIV in human body originated from .
A.animals B.plants
C.food D.Not mentioned in the article
38.Are the ten subtypes of the AIDS virus variation of one?
A.Yes. B.No.
C.Scientists are not sure about it at present.
D.It is not mentioned in the article.
39.Which of the following statements is true?
A.All the viral strains can be traced back to a single event.
B.HIV can not easily adapt to its surroundings.
C.AIDS started through contact with inflected monkeys in a remote area.
D.AIDS started through urbanization and mass inoculations.
40.Which of the following is the best topic for this passage?
A.How to Protect Yourself from AIDS?
B.Where Does HIV Come From?
C.Classification of HIV.
D.When Did AIDS Begin?
第6题
【C1】
A．trust
B．deny
C．refute
D．doubt
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