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 （）.
A.moon pool B.spider deck opening C.pontoon D.keyway
单项选择题 Most covered lifeboats will right themselves after capsizing if the（）.
单项选择题 Mean low water is the average height of（）.
单项选择题 In the Sargasso Sea there are large quantities of seaweed and no well defined currents. This area is located in the（）.
