单项选择题

It is implied that a modem farmer cannot simply move to another place when his field has become tired. This is because ______.

A．the production power of a new field is not higher than that of an old one
B．it takes a farmer more than ten years to cultivate a new field
C．the population of the world has increased rapidly
D．there will be too many grasses in a new field to grow crops

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单项选择题

From this passage it seems that ______.

A．Newton was not a successful scientist until he published his works
B．Newton was a scientist with at least three theories
C．Newton's theory was not accepted because Hooke did not approve it
D．Newton did not publish his theories because he was too disappointed

单项选择题

The evidence of this passage shows that ______.

A．the presently-accepted theory of light will soon be replaced by another new theory
B．scientists do not know enough to develop the most satisfactory theory of light
C．there would be no progress in our knowledge of light unless we questioned accepted theories
D．earlier scientists always aimed at the perfectness of a theory