列车施行常用制动时，货物列车运泞速度在（）以下时，不应缓解列车制动。
参考答案：15km/h
— When did you finish _____ your homework?
— I finished it at 9:00 last night. [ ]
A. do
B. to do
C. did
D. doing
压力容器年度检查以宏观检查为主。
