To expand the binomial expression (2x^3 + 3y^2)^7 using the binomial theorem, what should be substituted for the values of a and b?

a = 2x^3 and b = 3y^2
a = x^3 and b = y^2
a = 2x^10 and b = 3y^9
a = x^10 and b = y^9