many times, but he still doesn’t know how to operate the machine properly.
A. Although I have shown him
B. I have shown him
C. Having been shown
D. Having shown
网友回答
A. Although I have shown him
(答案→)B. I have shown him
C. Having been shown
D. Having shown
解析：考查句子结构。因为句子中有but,所以前面也应该是一个句子。答案为A。如果本题没有but,答案就应该是C。句意：我已经给他展示过很多次了，但是他仍然不知道怎么样恰当地操作机器。