They were walking along the shore a huge wave appeared out of nowhere, sweeping them out

They were walking along the shore a huge wave appeared out of nowhere, sweeping them out to sea.
A. as
B. while
C. when
D. though

A. asB. while(答案→)C. whenD. though解析：考查连词。As while when都表示当……时，区别是when 从句表示某时刻或一段时间，有“当……时”的意思；as 从句表示进展过程，有“随着，一边……一边”的意思；while 只表示一段持续的时间，有“在……的同时”的意思。Though的意思尽管。句意：当一个巨大的波浪突然凭空出现时，他们正在海岸上散布，把他们冲进了海里。都做有先后，故选C。

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