( )his telephone number, the manager had some difficulty getting in touch with the clerk.

问题描述:

( )his telephone number, the manager had some difficulty getting in touch with the clerk.
a.Not knowing
b.Knowing not
c.Not having known
d.Having not known
这道题选哪个,选它的原因是什么,谢谢~

A.表原因,没必要用完成式
bd形式不对.