Each AP uses 3 spatial streams, is 802.11ac-compatible and will operate at both 2.4GHz and 5GHz (since it is dual-band and has both 2.4GHz and 5GHz radios enabled). For 5GHz communications, it will operate optimally according to the 802.11ac standard: - Max data rate here is 6933.3Mbps, for max channel width of 160MHz and max of spatial streams of 8. - Since it is operating with a configured channel width of 40MHz (ie 1/4 of max channel width), and 3 streams (ie 3/8 of max spatial streams), its operating data rate is: 6933.3*(1/4)*(3/8) = 650Mbps For 2.4GHz communications, it will operate optimally according to the 802.11n standard (since 802.11ac does not support 2.4GHz): - Max data rate is 600Mbps, for max channel width of 40MHz and max spatial stream of 4. - Since it is operating with a channel width of 20MHz (ie 1/2 of max channel width) and 3 streams ( ie 3/4 of max spatial stream), its operating data rate is: 600*(1/2)*(3/4) = 225Mbps. Thus total data rate for communications on both bands = 875Mbps. We can then say that the 1Gbps is adequate. Hence D is correct.

Upgrading to 10Gbps is not the correct solution. They are using 802.11ac APs which in all probability do not support 10Gbps uplinks. 802.11ax APs are the first of their kind that support mGig ethernet. 802.11ac does not.

D is correct