单项选择题

There is much work to be done __________ we remember something forever.

A．after
B．when
C．unless
D．before
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单项选择题
A dolphin breathes through its __________.
A．mouth
B．ears
C．skin
D．blowhole
单项选择题
The dolphin's teeth __________.
A．are used to chew food
B．are all the same as the ape's
C．can swallow a whole fish
D．are used to catch food
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