Mr. White works for a chemical import-export company but he ______ for this industrial fa

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Mr. White works for a chemical import-export company, but he ______ for this industrial fair, since he is on leave.[1997]

A.has worked

B.works

C.has been working

D.is working

请帮忙给出正确答案和分析,谢谢!

热搜:a是b的充分条件,b是a的必要条件吗