单项选择题

The book is a ______ for students of science.

A．necessary
B．must
C．important
D．useful
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单项选择题
You are not a new member, are you ______. I joined only yesterday.
A．No, I'm not
B．Yes, I'm not
C．No, I am
D．Yes, I am
单项选择题
Which of the following factors is NOT mentioned as affecting the tide
A．the sun
B．the depth of the ocean
C．the moon
D．the winds
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