单项选择题

Scientists everywhere are trying to（）a cure for AIDS.

A．expect
B．invent
C．discover
D．make

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单项选择题

Tamara did not have time to go to the concert last night because she was busy（）for her lecture.

A．to preparing
B．to be prepared
C．preparing
D．being prepared

单项选择题

No sooner had we reached the top of hill（）we all sat down to rest.

A．when
B．then
C．than
D．until

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