Answer:
B & D
Explanation:
It can-t be A, because that would mean 20², which equals 400, would equal 20.
B is correct because even though it's negative, negative times negative = positive, which would mean that (-sqrt of 20)(-sqrt of 20)=20.
C is wrong because sqrt -20 is an imaginary number,which is a completely different topic.
D is correct because it's the same thing as B, but without the 2 negaties cancelling each other out.
E is the same as A, except it's '-20' x '-20', whcih is still 400, which is still wrong
Hope this helps :)