紧急放风阀的作用位置有（）
A.充气缓解位
B.常用制动位
C.常用保压位
D.紧急制动位
参考答案：A, B, D
Don't expect too much of them.They are suffering from a _________ of money themselves. [ ]
A. possibility
B. poverty
C. similarity
D. property
简述DBMS的功能。
