单项选择题 A thrust block is designed to（）.

单项选择题 A thin，whitish，high cloud popularly known as “mares’ tails” is（）.

单项选择题 A tank 36 ft. by 36 ft. by 6 ft. is filled with water to a depth of 5 ft. If a bulkhead is placed in the center of the tank running fore-and-aft along the 36-foot axis，how will the value of the moment of inertia of the free surface be affected?（）