单项选择题

A.锋电位 B.阈电位
C.负后电位 D.局邮电位
E.正后电位
可兴奋细胞受到刺激后,首先可出现
A.
B.
C.
D.
E.

A.锋电位
B.阈电位
C.负后电位
D.局邮电位
E.正后电位
可兴奋细胞受到刺激后,首先可出现
A.
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单项选择题

Man and Computer
What makes people different from computer programs? What is the missing element that our theories don't yet(51)for? The answer is simple: People read newspaper stories(52)a reason to learn more about what they are interested in. Computers, on the other hand, don't. In fact, computers don't(53)have interests; there is nothing in particular that they are trying to find out when they read. If a computer(54)is to be a model of story understanding, it should also read for a 'purpose'.
Of course, people have several goals that do not make(55)to attribute to computers. One might read a restaurant guide in order to satisfy hunger or entertainment goals, or to(56)a good place to go for a business lunch. Computers do not(57), and computers do not have business lunches.
However, these physiological and social goals give(58)to several intellectual or cognitive (认知的) goals. A goal to satisfy hunger gives rise to goals to find(59)about the name of a restaurant which serves the desired type of food, how expensive the restaurant is, the(60)of the restaurant, etc. These are goals to(61)information or knowledge, what we are calling(62)goals. These goals can be held by computers too a computer might 'want' to find out the location of a restaurant, and read a guide in order to do so(63)the same way as a person might. While such a goal would not(64)out of hunger in the case of the computer, it might(65)rise out of the 'goal' to learn more about restaurants.
A.express
B.explain
C.account
D.count

A.
Of
B.
However,
C.
A.express
B.explain
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单项选择题

Escaping from the Earth
The Earth has a force that pulls things toward itself. We call this force gravity(地心引力). This is something we live with all the time, and we take it for granted and hardly ever think about it. But it is a most important factor in rocket operation and must be overcome if we are to get anywhere in space, or off the ground at all.
Take the throwing of a hall as an example. The harder the ball is thrown, the faster and higher it will go. What is the secret? Its speed. If we could throw the ball hard enough it would go up and up forever and never come down. The speed at which it would have to be thrown to do this is known as escape speed. Of course, we cannot throw a ball hard enough because the speed required to escape completely from the Earth's gravity is seven miles per second, or over twenty-five thousand miles per hour.
Once escape speed has been reached by a spacecraft(宇宙飞船), no further power is needed. A rocket aimed at the Moon, for instance, will 'coast'(滑行) the rest of the way be cause the Earth's gravity cannot then pull it back, and there is no air resistance(阻力) in space to slow it down. This 'coasting' is known as 'free fall'. That does not mean the rocket is falling down towards the Earth but that it is traveling freely in space without the aid of power, like a bicycle coasting downhill.
Free fall is an important feature of space travel: it would be impossible to carry enough fuel to provide powered flight all the time.
What is the most important factor for a rocket to escape from the Earth?
A.To travel as fast as it can.
B.To overcome the Earth gravity.
C.To get away from the air resistance.
D.To have strong power in its operation.

A.
Take
B.
Once
C.
Free
D.
What
E.To
F.
B.To
G.
C.To
H.
D.To
I.
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