Hi I really need help with this question(It's my last one on this quiz)PLEASE HELP) 20 POINTS!!!

Darius uses the polynomial identity (x-y)^2=x^2-2xy+y^2 to show that 9^2=81
what values can Darius use for x and y?
A) x=81 and y=0
B)x=3 and y=6
C)x=11 and y=2
D)x=9 and y=81