Okay, here we have this:
Considering the provided information we obtain that:
As a-b=0, then a=b.
And as a=b, in the expression ab, we can replace "b" and we have that: ab=aa, and finally simplifying:
aa=a².
So in summary we have:
ab
=aa
=a².
Finally we obtain that the correct answer is tha option A.
