Busy and successful as he was, the novelist was willing to _____ any promising young man and give him

all the help he could. [ ]

A. take up

B. pick up

C. make up

D. look up

唯一一种支持基于用户名和密码验证的二层协议是（）。

A.HDLC

B.以太

C.PPP

D.ATM