I'm sorry you've been waiting so long, but it'll still be some time _____ Brian gets back. [ ]

A. before

B. since

C. till

D. after

( )为负值时，即表示项目运行超出预算费用，当其为正值时，表示项目运行节支，实际费用没有超出预算费用。

A．费用偏差

B．进度偏差

C．费用绩效指数

D．进度绩效指数