单选题 The most significant limitation of VHF signals is that they （ ）.

单选题 If the pilot wants to receive full ATC services, particularly in busy environment, （ ） transceivers are a necessity.

单选题 A radio system that combines a transceiver for normal two-way communications and a navigational aid receiver into a single unit is called a （ ）.

单选题 The frequency band most used general aviation for two-way voice communications is （ ）.

单选题 If the transceiver has only 360-channel, （ ）.

单选题 A radio that combines a transmitter and recevier in one unit is called a （ ）.

单选题 Constant attention to correct phraseology and procedures will （ ）.

单选题 ICAO adopted a phonetic alphabet to be used in radio transmissions in order to （ ）.