单项选择题

Wind motion can be observed in the atmosphere by ______ the trails of meteors passing through it.

A．to watch
B．watching
C．watched
D．watch
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单项选择题
In such a changing and complex society, formerly simple solution to informational needs become ______.
A．confusing
B．acceptable
C．complicated
D．feasible
单项选择题
A．concentrateB．chewC．fixD．taste
A．concentrate
B．chew
C．fix
D．taste
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