________ many times，I still didn't know how to operate the machine.A．Having taug_刷题宝

题干

________ many times，I still didn't know how to operate the machine.

A．Having taught

B．Having been taught

C．Being taught

D．Teaching

上一题下一题 0.64难度单项选择更新时间:2013-05-19 12:19:51

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