--- The young man spent as much time as he _______ the experiments.

--- No wonder he succeeded _______.

A．did; by the end

B．could doing; in the end

C．could doing; at the end

D．could to do; in the end

L2TP隧道和会话的建立流程都是通过（）完成的。

A.二次握手

B.三次握手

C.四次握手

D.以上答案均不正确