Question 1074887
A. The output of the operation is contained in G.
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B. Because
a#a=a#a=a
a#b=b#a=b
a#c=c#a=c
a#d=d#a=d
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C. b#c=d
c#b=d
So b#c=c#b.
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You can do the other case. 
Just look for any other combination but don't use a in the operation since it's the identity element.