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B In July 1994 Jupiter, the largest planet in our solar system, was struck by 21 pieces o

B

In July 1994 Jupiter, the largest planet in our solar system, was struck by 21 pieces of a comet (彗星). When the fragments (碎片) landed in the southern part of the giant planet, the explosions were watched by scientists here on earth. But what if our own planet was hit by a comet?

The year is 2094. It has been announced that a comet is heading towards the Earth. Most of it will miss our planet, but two fragments will probably hit the southern part of the Earth. The news has caused panic.

On 17 July , a fragment four kilometers wide enters the Earth ' s atmosphere with a huge explosion. About half of the fragment is destroyed. But the major part survives and hits the South Atlantic at 200 times the speed of sound. The sea boils and an enormous wave is created and spreads.

The wall of water rushes towards southern Africa at 800 kilometres an hour. Cities on the African coast are totally destroyed and millions of people are drowned. The wave moves into the Indian Ocean and heads towards Asia.

Millions of people are already dead in the southern part of the Earth, but the north won' t escape for long. Tons of broken pieces are thrown into the atmosphere by the explosions. As the sun is hidden by clouds of dust, temperatures around the world fall to almost zero. Crops are ruined. Wars break out as countries fight for food. A year later civilization has collapsed. No more than 10 million people have survived.

Could it really happen? In fact, it has akeady happened more than once in the history of the Earth. The dinosaurs(恐龙)were on the Earth for over 160 million years. Then 65 million years ago they suddenly disappeared. Many scientists believe that the Earth was hit by a space fragment.

The dinosaurs couldn ' t survive in the cold climate that followed and they became extinct. Will we eet the same end?

61. Which of the following is NOT TRUE according to the author ' s description of the disaster in 2094?

[ A] The whole world becomes extremely cold.

[ B ] All the coastal cities in Africa are destroyed.

[ C] The whole mankind becomes extinct.

[ D] The visit of the comet results in wars.

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第1题

步进电机和伺服电机的区别有哪些()

A.伺服电机比步进电机过载能力强

B.伺服电机比步进电机控制精度更高

C.伺服电机比步进电机响应速度更快

D.伺服电机是闭环控制步进电机一般是开环控制

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第2题

在TBA22机器上使用的电机有哪几种()

A.伺服电机

B.步进电机

C.直流电机

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第3题

下列哪些电机的负载特性比较硬()

A.步进电机

B.伺服电机

C.交流异步电机

D.空心杯伺服电机

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第4题

夹爪驱动电机为()电机,终端驱动电机为()电机,调纸管位置电机为()电机,容量调整电机为()电机,双氧水泵电机为()电机。()

A.直流、交流同步、交流异步、伺服、交流异步

B.单相交流、步进电机、交流异步、伺服、伺服

C.伺服、伺服、步进电机、交流异步、伺服

D.伺服、伺服、步进电机、步进电机、交流异步

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第5题

夹爪驱动电机为()电机,终端驱动电机为()电机,调纸管位置电机为()电机,容量调整电机为()电机,双氧水泵电机为()电机。()

A.直流、交流同步、交流异步、伺服、交流异步

B. 单相交流、步进电机、交流异步、伺服、伺服

C. 伺服、伺服、步进电机、交流异步、伺服

D. 伺服、伺服、步进电机、步进电机、交流异步

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第6题

下列哪些电机的负载特性比较硬()

A.步进电机

B.伺服电机

C.交流异步电机

D.空心杯伺服电机

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第7题

常用的位移执行机构有步进电机、直流伺服电机和交流伺服电机。 ()

常用的位移执行机构有步进电机、直流伺服电机和交流伺服电机。 ( )

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第8题

同等条件下,伺服电机控制精度比步进电机高()
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第9题

常用的位移执行机构有步进电机、直流伺服电机和交流伺服电机()

常用的位移执行机构有步进电机、直流伺服电机和交流伺服电机()

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第10题

常用的位移执行机构有步进电机、直流伺服电机和交流伺服电机。 ()

常用的位移执行机构有步进电机、直流伺服电机和交流伺服电机。 ( )

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