问题
选择题
We _______ on it for several hours but we have not yet reached any conclusion.
A．work
B．areworking
C．havebeenworking
D．havebeenworked
答案
答案：C
答考查时态。根据but后时态，可以判断出到现在还没有得出结论，有可能还要继续下去，所以要现在完成进行时。
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