Answer:
A.radio waves
Step-by-step explanation:
To make this system work we need a transmitter and a receiver. Transmitter will send the signal in the form of electromagnetic wave and there must be a sensor at the receiver end to receive it.
In the given scenario only radio waves can be practically used. In all other radiation we need a direct line of sight between the transmitter and receiver for the signal to transmit properly. While the rocket is in flight this is not possible. So best and the only option would be to use radio waves. Once transmitted the radio signals will be all around and the receiver can easily pick up the signal and work accordingly.