气体冷却器作用（）。
A.将来自真空槽的气体冷却至300℃以下
B.减轻真空泵的负荷
C.粗除尘作用
D.抽真空
E.分析气体成分
参考答案：A, B, C
如果多项式x2-（a+5）x+5a-1能分解成两个一次因式（x+b）（x+c）的乘积，b、c为整数，则a的值是多少？
---- How did her family feel when you visited them?
---- My coming ________ the happiness of her family.
A．added up to
B．added up
C．added
D．added to
