In 802.11n, what is the difference between HT20 and HT40 operation?

A.
HT40 corresponds to a 40Mbps PHY rate, while HT20 uses a 20Mbps PHY rate

B.
20 MHz wide channels are used with HT20, while 40 MHz channels are used with HT40

C.
HT20 uses 2 spatial streams, while HT40 uses 4 spatial streams

D.
HT20 uses a short guard interval while HT40 uses a long guard interval

Explanation: