What must occur before a STA operating in an HR-DSSS BSS can transmit a frame over the wireless medium?

A.
Its NAV must be equal to zero.

B.
It must receive a CF-Poll frame from the access point.

C.
The appropriate interframe space must expire.

D.
Its Backoff timer must expire.

E.
Its CCA must report that the medium is idle.

F.
The AP must issue the STA a TXOP.