单项选择题
A.rolling B.rolls C.rolled D.roll
You should keep national flag（）.A.flyingB.flewC.flownD....
单项选择题You should keep national flag（）.
A.flying B.flew C.flown D.flies
You should slack the mooring lines （）when the wind is b...
单项选择题You should slack the mooring lines （）when the wind is big.
A. at the same time B. on time C. in time D. at times
We must （）to inspect the problems about the safety of f...
单项选择题We must （）to inspect the problems about the safety of fire prevention.
A.prepares B.preparing C.prepared D.prepare
