单项选择题

In vain______ to get in touch with the authorities.

A．they tried
B．did they try
C．they have tried
D．the had tried
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单项选择题
Language, culture, and personality may be conceded ______of each other in thought, but they are inseparable in fact.
A．indistinctly
B．independently
C．separately
D．irrelevantly
单项选择题
The largest system serving e-mail messengers is the Internet, a______ of millions of computers linked worldwide.
A．unity
B．combination
C．network
D．connection
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