单项选择题
A wooden plug fitted tightly in the vent of a damaged tank may prevent the tank from（）.
A.filling completely B.developing free surface C.developing free surface moment D.collapsing
单项选择题 A tackle is two blocked when the blocks are（）.
单项选择题 A sweep oar is an oar that is（）.
单项选择题 A stopper is（）.
