________ several times, but he still doesn't know how to do it properly．

________ several times, but he still doesn't know how to do it properly．

A.Being shown

B.Having shown

C.Having been shown

D.I've shown him

答案及解析： D

解析：

考查谓语动词和非谓语动词的区别。根据题干中的but可知这是一个由转折连词连接的两个句子，因此要选谓语动词而不选非谓语动词。本题中如果去掉but则答案为C。