What is the best practice for configuring data rates for an 802.11a VoWLAN deployment?

What is the best practice for configuring data rates for an 802.11a VoWLAN deployment?

A.
Configure mandatory data rates of 9 and 54 Mb/s. Disable data rates below 6 Mb/s and all
other data rates as supported.

B.
Configure a mandatory data rate of 6 Mb/s. Disable data rates below 6 Mb/s and configure all
other data rates as supported.

C.
Configure a mandatory data rate of 54 Mb/s. Disable data rates below 36 Mb/s and configure all
other data rates as supported.

D.
Configure a mandatory data rate of 12 Mb/s. Disable data rates below 12 Mb/s and all other
data rates as supported.

Explanation: