排水系统的起点是( )。 A．卫生器具 B．存水弯 C．排水管道系统 D．通气管系

10箱苹果，如果每箱以30千克为准，超过的千克数记作正数，不足的千克数记作负数，称重的记录如下：+2，+1，0，-1，-1.5，-2，+1，-1，-1，-0.5．这10箱苹果的总质量是多少千克？

____________ stand up. Please sit down.[ ]

A. Doesn't

B. not

C. Don't

D. Do

先化简，再求值：3a²b-[2a²b-（2ab-a²b）-4a²]-ab，其中a=-3，b=-2

Fifty applicants for a job were given scores from 1 to 5 on their interview performance. Their scores are shown in the table above. What was the average score for the group ？（）

A. 2.79

B. 2.86

C. 2.91

D. 2.99

E. 3.03

资本的( )是经济发展的重要问题。

A．收入和支出

B．筹集和配置

C．收入和配置

D．筹集和支出