Question

________ 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

Answer 1

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。