A.warmer，less dense，and less stableB.cool，more dense，an……

单项选择题Commercial ships or other persons or agencies requiring the assistance of Canadian Coast Guard icebreakers should first contact（）.

A.the Canadian Coast Guard
B.Ice Sarnia
C.the Ice Navigation Center
D.the icebreaker assigned to the area

单项选择题Coiling new rope against the lay，bringing the lower end up through the center of the coil，then coiling with the lay，in order to remove the kinks，is known as（）.

A.coiling
B.faking
C.flemishing
D.thoroughfooting

单项选择题Coast Pilots and navigational charts are kept corrected and up-to-date by using the（）.

A.pilot charts
B.Notices to Mariners
C.Tide Tables
D.Current Tables

单项选择题Clouds with the prefix “nimbo” in their name（）.

A.are sheet or layer clouds
B.have undergone great vertical development
C.are middle or high altitude clouds
D.are rain clouds

单项选择题Clouds form（）.

A.as a mass of warm，humid air rises into the atmosphere and cools，condensing moisture into small droplets
B.as winds blow across bodies of water，the sun causes the moisture to be absorbed and move upward forming clouds
C.dry air compresses moisture from the atmosphere into clouds
D.when the relative humidity of the atmosphere is low