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Is it just me or are a lot of these questions poorly worded?

Chapter 18 question 2:

"How can a MIMO system increase throughput at the Physical layer? (Choose all that apply.)"

A. Spatial multiplexing

B. A-MPDU

C. Transmit Beamforming

D. 40 MHz channels

E. Dual-CTS protection

I chose AC. The answer is supposedly ACD with the explanation "...40 MHz HT channels effectively double the frequency bandwidth, which results in greater throughput."

Because the question specifically called out MIMO as opposed to 802.11n, I only selected the answers that pertained to MIMO technology (of which 40 MHz channels is not one of them). Very misleading!!

I don't know if I would call it VERY misleading, but I do see your point.  

However, I couldn't find any 802.11 MIMO standards that do not include 40 MHz channels, even with single stream radios.  There are manufacturers who don't enable it, even when the original chipset (e.g. some Marvell chips) support it in 2.4 GHz.

Under what I call a good neighbor policy, I think it is rude for anyone to use 40 MHz wide signals in the 2.4 GHz band.