A time diagram is a diagram of the celestial sphere as observed from above the（）.

A tug is “in irons” when held in a fixed position by（）

A stand-on vessel is（）.

A time diagram is a diagram on the plane of the（）.

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

A tug is best positioned for towing and maneuvering on rivers and other restricted waters where wave action is limited when（）.

A type of precipitation that occurs only in thunderstorms with strong convection currents that convey raindrops above and below the freezing level is known as（）.

A swift current occurring in a narrow passage connecting two large bodies of water，which is produced by the continuously changing difference in height of tide at the two ends of the passage，is called a（）.

A tow of 9 barges is made up three abreast by three long. The towboat is faced up to the last barge of the center string. The outer two strings of barges are the（）.

A strong，often violent，northerly wind occurring on the Pacific coast of Mexico，particularly during the colder months，is called（）.