单项选择题
The Earth’s irregular heating is caused by （）.
A.the time of day B.the seasons C.geography D.All of the above
单项选择题 The Earth has the shape of a(n) （）.
单项选择题 The distance from the still water level (corrected for tides and storm surge) to the bottom of the hull of a ship is the（）.
单项选择题 The distance between the surface of the water and the tidal datum is the （）.
