“______something valuable and throw the rest away,”the mother asked her children when they were cleaning the old house.

A．Pick up

B．Pick out

C．Pick from

D．Pick off

在软件生命周期中，能准确地确定软件系统必须做什么和必须具备哪些功能的阶段是 ______。

A．概要设计

B．详细设计

C．可行性分析

D．需求分析