单项选择题

Before the drug is used on human beings, experts have to ______ dogs.

A. be experimented
B. experiment
C. experiment with
D. experiment on
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单项选择题
We forgot to bring our tickets, but please let us enter, ______
A. do you
B. can we
C. will you
D. shall we
单项选择题
______ he has limited technical knowledge, the old worker has a lot of experience.
A. Since
B. Unless
C. As
D. Although
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