When using the binomial formula, which of the following is a correct step in the expansion of (x+y) ^4?

(X+y) ^2 (x+y) ^2

(X^2+2xy+y^2) (X^2+2xy+y^2)

X^2 (x^2+2xy+y) + 2xy (x^2+2xy+y) + y^2 (x^2+2xy+y)

X^4+4x^3y+6x^2y^2+4xy^3+y^4 is the answer. i didn't write all the steps as I would have been too long and complicated