4．飛機 selective call system 是用做：
(A)地面呼叫飛機‧Ground call aircraft.
(B)飛機呼叫飛機‧Aircraft call aircraft.
(C)通話系統‧Interphone system.
(D)導航系統‧Navigation system.

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統計： A(0), B(1), C(0), D(0), E(0) #2087148