Which statement is correct about a WLAN RF medium?

Which statement is correct about a WLAN RF medium?

A. A WLAN RF is a full duplex, contention free medium where each client transmits on a separate channel. B. A WLAN RF is a full-duplex, contention-free medium where 802.11 stations can transmit and receive at the same time. C. A WLAN RF is a half-duplex, shared medium where 802.11 stations contend with each other for access. D. A WLAN RF is a half-duplex, contention-free medium where the access point polls each station in turn.