单项选择题

An ignorant farmer will make the land poorer______.

A．ff he lets dead leaves decay in the soil by themselves
B．if he makes the humus decrease after taking away his crops
C．by clearing away all the dead leaves
D．by burning waste plant material lying about
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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
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