问题

Scientists ______ SARS for several monthsbefore a major discovery was made in the field.

A:had been studying
B:have been studying
C:have studied
D:are studying

正确答案是：

同类题型

is needed in the whole society, which requirespcantrust them.

We have time and again ____our position on Taiwan issue! Whatever happens, we won’t change it!

The part of the apple is bad, please___________.

下列各句中，表达得体的一句是

theroad ________ with snow, they had to stay at home, watching TV and drinkingcoffee.