Explain how the quotient of powers property was used to simplify this expression.

a: by simplifying 9 to 3^2 to make both powers base three and adding the exponents

b: by simplifying 9 to 3^2 to make both powers base three and subtracting the exponents

c: by finding the quotient of the bases to be 1/3 and simplifying the expression

d: by finding the quotient of the bases to be 1/3 and cancelling common factors