In the following four descriptions about random access protocol, which one is NOT correct?

A. In slotted ALOHA, nodes can not transmit at random time.
B. In pure ALOHA, if a frame experiences a collision, the node will retransmit it immediately with probability p.
C. The maximum efficiency of a slotted ALOHA is higher than a pure ALOH
D. In slotted ALOHA, no node listens to the channel before transmitting.