单项选择题

Scientists say it may be five or six years （） this medicine is tested on human beings.

A．since
B．before
C．after
D．when

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单项选择题
（） the obvious differences in size and population, the states of America have many things （） common.（）

A．Although; on
B．Though; in
C．Despite; in
D．Because of; on
单项选择题
A club is a place to make frequent（） with friends.

A．accounts
B．attempts
C．contents
D．contacts
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