不属于离心式空气压缩机内部的迷宫密封是（）
A、轴封装置
B、级间密封
C、轮盖密封
D、平衡盘密封
参考答案：A
There are certain _______when you have to interrupt people who are in the middle of doing something.
A．chances
B．situations
C．occasions
D．opportunities
