In exercise condition, cardiac output is mainly regulated by

A、homometric regulation

B、heterometric regulation

C、preload

D、afterload

The passage is mainly about ______.

A．the high injury rates for those doing exercises

B．the ways to avoid exercise injuries

C．the evidences for the seriousness of exercise injuries

D．the studies about injury rates and causes for injuries

The passage is mainly about ______.

A．the high injury rates for those doing exercises

B．the ways to avoid exercise injuries

C．the evidences for the seriousness of exercise injuries

D．the studies about injury rates and causes for injuries

The passage is mainly about ______.

A．the high injury rates for those doing exercises

B．the ways to avoid exercise injuries

C．the evidences for the seriousness of exercise injuries

D．the studies about injury rates and causes for injuries

The passage is mainly about ______.

A．the high injury rates for those doing exercises

B．the ways to avoid exercise injuries

C．the evidences for the seriousness of exercise injuries

D．the studies about injury rates and causes for injuries

The pausage is mainly about_________． A．the high injury rates forthose doing exercises B．the ways to avoid exerciseinjuries C．the evidences or the seriousness of exercise injuries D．the studies about injuryrates and causes for injuries

The passage is mainly about ______.

A．how to keep fit

B．how to lose weight

C．the benefits brought about by regular exercises

D．exercises and diet

Writing exercises like copying， fill-in， completions and transformation are mainly the type of exercises used in_________

A.controlled writing

B.guided writing

C.free writing

D.expressive writing

The passage is mainly concerned with______.

A．stress

B．physical exercises

C．diets

D．anxiety

It is clear that some people who participate in exercise training will develop injuries to their bones, muscles, and joints(关节). Despite unfounded reports in the mass media of extremely high injury rates among adult exercisers, there have been few good studies of exercise injuries in populations. One of the difficulties in performing such studies has been the need to identify both the number of cases and the number of people at risk for injury. In other words, it is difficult to know the number of individuals injured and the total number of individuals exercising in the population. But these two figures are necessary in order to calculate(统计) true injury rates. Normally, injury is defined as an accident that causes a person to stop exercising for at least one week. The best available studies on injury rates show that about 25 to 30 percent of adult runners become "injured" (based on the above definition) over the course of a year. More serious injuries include those for which the injured person seeks medical care. If only they are considered, injury rates are much lower, perhaps in the range of 1 percent per year.

Little is known about the causes of exercise injuries. One factor that has been linked to injury is the amount of exercise; for example, individuals who run more miles are likelier to be injured than those who run fewer miles. Factors such as age, sex, body type, and experience have not been shown to be associated with risk of injury. It seems logical that structural abnormalities, sudden increases in training intensity, and types of equipment used are likely to be related to injury risk. However, data to support these opinions are not available.

What is the writer's attitude towards high injury rates among adult exercisers reported by the mass media?

A．Positive.

B．Indifferent.

C．Negative.

D．Reserved.