What statement is true concerning the use of Orthogonal Frequency Division Multiplexing (OFDM) modulation method in IEEE 802.11 WLANs?

What statement is true concerning the use of Orthogonal Frequency Division Multiplexing (OFDM) modulation method in IEEE 802.11 WLANs?
A . OFDM implements BPSK modulation to allow for data rates up to 7 Gbps.
B . OFDM was first introduced in 802.11a and is used by the ERP, HT and VHT PHYs as well.
C . OFDM modulation is used only in 5 GHz 802.11 transmissions.
D . OFDM was used by Frequency Hopping Spread Spectrum (FHSS) PHY devices.

Answer: B