many times，I still didn't know how to operate the machine.
A. Having taught
B. Having been taught
C. Being taught
D. Teaching
网友回答
A. Having taught
(答案→)B. Having been taught
C. Being taught
D. Teaching
解析：考查分词做状语。本句中的动词teach与句子主语I构成被动关系，可以使用过去分词done表示被动和已经完成；过去分词done=having been done；后者强调的是已经完成，前者强调的是被动。教育：已经被多次教育，我仍然不知道如何操作这部机器。故B正确。