Which statement best describes the ability of a wireless client to access and transmit a data frame to an AP?

Which statement best describes the ability of a wireless client to access and transmit a data frame to an AP?
A . The client listens to the media until polled by the AP using PCF to send its data.
B . The client listens to the media until a data frame is finished, at which time it transmits, unless a collision of data frames has occurred.
C . The client uses random countdown timers to start the transmission of a data frame.
D . The client listens to the media and countdown timers to start the transmission of a data frame.

Answer: D