Given: While using the EDCA access mechanism, QoS STAs and QoS APs must use a backoff algorithm in order to arbitrate for medium access. The backoff procedure includes randomly choosing an integer from the contention window.

When may QoS STAs and QoS APs decrement their randomly chosen Backoff Time?

A.
Only during the Contention Free Repetition Interval

B.
Only when the medium is considered idle

C.
During every PCF Interframe Space (PIFS)

D.
Immediately following a DTIM Beacon

E.
Immediately preceding a TBTT