Mr.White works with a chemicals import&export company,but he______for this industrial fair,since he is on leave.a.has worked b.worksc.has been working workingThe answer is D,please give an explaination!Why not chooseA?
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选C，因为A代表现在已经完成，也就是目前已经不在做了而c意思是到现在还一直在做，从过去开始做外贸一直延续到现在，当前