（）_________do you change the cell for your watch？
A. How many
B. How often
C. How little
D. How Soon
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The speaker，________for his speeches，was warmly received by the students．
A. known
B. to be known
C. having known
D. being known
During the Ice Ages，man developed the use of tools，and this is a way of protecting himself
A. conflicts
B. hazards
C. faults
D. shortcomings
函数y=2x3-x2+1在x=1处的导数为（） (A)2 (B)3 (C)4 (D)5
Work hard ________ you will overcome the difficulties．
A. so
B. and
C. for
D. but
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