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.