The height of a light is measured from which reference plane?（）

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) （）.

A.sphere
B.oblate spheroid
C.spheroid of revolution
D.oblate eggoid

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（）.

A.air gap
B.freeboard
C.penetration
D.water depth

单项选择题The distance between the surface of the water and the tidal datum is the （）.

A.range of tide
B.height of tide
C.charted depth
D.actual water depth

单项选择题The distance between any two meridians measured along a parallel of latitude and expressed in miles is the （）.

A.difference in longitude
B.mid-longitude
C.departure
D.meridian angle