21．读图，回答下列问题。（共20分，除特别说明外，每空2分）

（1）图中A地的水循环类型主要是________循环，B地的水循环类型有________循环和________循环。

（2）a、b两条河流中，水量较稳定的是___河，判断依据是_______          _。（3分）

（3）甲、乙两城市中，水资源较丰富的是_____城市，原因是______                       _。（3分）

（4）水循环得以顺利完成的内因是___________；外因__________。

Fire protection and manning regulations for towing vessels state that the Master or person in charge must ensure that all crew members who have not participated in the drills or received the safety orientation（）.

A.receive a safety orientation or view a videotape before the vessel gets underway

B.view a videotape on safety procedures within 48 hours of reporting for duty

C.receive a safety orientation within 24 hours of reporting for duty

D.none of the above