Steve was busy clearing the cups and dishes from the table ________ others were playing.

A．until

B．if

C．since

D．while

决策支持系统主要支持以下哪类决策问题

A．定性决策与结构化决策

B．定量决策与半结构化决策

C．半结构化与非结构化决策

D．结构化与半结构化决策