What is the meaning of carrier sense in the CSMA/CD algorithm?

What is the meaning of carrier sense in the CSMA/CD algorithm?
A . The host will retransmit the frame if it detects a collision during transmission.
B . The host is able to detect the transmission speed of the Ethernet switch port to which the host is connected.
C . The host will only transmit data when it detects that no other devices are transmitting.
D . The host will only transmit upon a timer expiry.
E . The host will only transmit when it receives the token.

Answer: C