设f(x)=x2(x-1)(x-2)，则f'(x)的零点个数为______．
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What were the men doing according to the police
A. They were treating industrial waste.
B. They were tanking industrial waste.
C. They were tanking chemicals.
D. They were using a tank to mix chemicals.
It has been estimated that the earth's surface temperature has increased ______ one quarter to three quarters of a degree since 1850. ~
A. to
B. by
C. at
D. with
What Can we infer about the woman
A. That she has stopped smoking.
B. That she does not want to get married.
C. That she has asked the man to quit smoking many times.
D. That she is not in love with the man.
What was the author's purpose when writing this passage
A. To give practical instruction for pruning a tree.
B. To give a gardener description of pruning.
C. To explain how trees develop disease.
D. To discuss different methods of prunin
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