When communicating on the radiotelephone using plain English，what procedure word indicates the end of my transmission and that a response is necessary? （）

单项选择题To reduce the amount of catenary you may（）.

A.shorten the hawser or increase the tug's speed
B.lengthen the hawser or reduce the tug's speed
C.place your tug in irons
D.make a sharp turn

单项选择题The Vessel Bridge-to-Bridge Radiotelephone Act applies to which towboat?（）

A.A 100 GT towboat，24 feet in length
B.A 90-foot towboat tied to the pier
C.A 60-foot towboat towing by pushing ahead
D.A 400 GT towboat anchored

单项选择题The Vessel Bridge-to-Bridge Radiotelephone Act applies to（）.

A.every towing vessel of 16 feet or over in length while navigating
B.every vessel of 50 GT and upward，carrying one or more persons for hire
C.all aircraft operating on the water
D.every power-driven vessel of 20 meters and upward while navigating

单项选择题The unit of duration of a dash in Morse Code is（）.

A.one and one-half times the length of a dot
B.twice the length of a dot
C.three times the length of a dot
D.four times the length of a dot

单项选择题The range of a SSB transmission is MOST affected by（）.

A.atmospheric noise and radiated power
B.the frequency band selected and time of day or night
C.interference and position of the moon
D.radiated power and nearness to shore