单项选择题
A.stream the sea anchor
B.take an anti-seasickness pill
C.open the pressure relief valve
D.drink at least one can of water
单项选择题 Normal pool elevation is the height in feet of the section of river above a dam. This height is measured from（）.
单项选择题 Most drill ships and barges have a walled opening below the derrick，open to the water’s surface and through which various drilling tools can pass down to the sea floor called a （）.
单项选择题 Most covered lifeboats will right themselves after capsizing if the（）.