—Nobody knows _____ he was after he graduated from Beijing University.

—But I was once told he was a doctor working in a far-away village. [ ]

A. what

B. who

C. where

D. how

在工程网络计划工期优化过程中，当出现两条独立的关键线路时，在考虑对质量和安全影响差别不大的基础上，应选择的压缩对象是分别在这两条关键线路上的两项( )的工作组合。

A．直接费用率之和最小

B．资源强度之和最小

C．持续时间总和最大

D．间接费用率之和最小