题目内容

________ several times,but he still doesn't know how to do it correctly.
A.Although I've taught him
B.I've taught him
C.Having been taught
D.Having taught
B
although不能与but连用,故不能选择A。若选C,必须把并列连词but去掉,这样就变成了一个简单句,为现在分词短语作让步状语。
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