泵的汽蚀余量分为（）、（）。
参考答案：有效汽蚀余量；必须汽蚀余量
The patient's legs were so weak and he could stand_______. [ ]
A. sometimes
B. hardly
C. often
D. ever
海关批准保税的范围包括批准成立保税仓库、保税工厂和保税集团。 ( )
