A multiple access scheme which listens to the channel to make sure it is empty, prior to transmitting, is called ...

Answer: Taking turns protocol

Explanation: Taking turns protocol is the protocol that belongs to the class of the MAC (Media Access Control) protocol. This protocol has the mechanism of working by giving the notation about the turn of which channel is to be sent. This protocol's operation is deciding turn of channel and ensuring that it is empty before sending it and decides the after travelling of one channel from the source to destination, next channel that should travel through the path.