We on it for many hours but we have not yet reached any conclusion.

admin2010-06-03  46

问题 We      on it for many hours but we have not yet reached any conclusion.

选项 A、work
B、have been worked
C、have been working
D、are working

答案C

解析 现在完成进行时表示动作从过去某一时间开始一直延续到现在或离现在不远的时间。本题中表示”好几个小时”以来一直在做某事,因此用现在完成进行时。
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