河南成教 / 大学英语4
正确率：100%
3[单选题]
__________ how to operate a switchboard, I had to ask the office supervisor to show me the correct procedures.
A.Not known
B.Not to know
C.Not knowing
D.Having not known
__________ how to operate a switchboard, I had to ask the office supervisor to show me the correct procedures.
参考答案：