问题
选择题
_____ 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
答案
答案：B
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。
