B, III only.
III is pretty easy.
The product of 20! will be even, so adding 21 to it makes it odd. Hence, not a product of 2.
I and II are a little trickier
The product of 20! will be divisible by 7 and 21, as both of those quantities can be pulled out of the factors of 20!. (i.e. 7 and 14*3 give us what we need) Adding 21 to 20! keeps those same factors, since 21 is divisible by both 7 and 21.
This means 7 and 21 are both factors of "20!+21" leaving only 2 as a non factor
III is pretty easy.
The product of 20! will be even, so adding 21 to it makes it odd. Hence, not a product of 2.
I and II are a little trickier
The product of 20! will be divisible by 7 and 21, as both of those quantities can be pulled out of the factors of 20!. (i.e. 7 and 14*3 give us what we need) Adding 21 to 20! keeps those same factors, since 21 is divisible by both 7 and 21.
This means 7 and 21 are both factors of "20!+21" leaving only 2 as a non factor
![FLO – Therapy at the Club – Pre-Single [iTunes Plus M4A]](http://is1-ssl.mzstatic.com/image/thumb/Music221/v4/a4/11/88/a41188ed-0f2e-e8d5-1163-d59e373cc58c/26UMGIM30046.rgb.jpg/208x208bb.webp)
.jpg)
