The correct option is A (bx+ay)(ax+by)
Given expression: ab(x2+y2)+xy(a2+b2)
By applying the distributivity property we get,
=abx2+aby2+a2xy+b2xy
By regrouping the terms we get,
=(abx2+a2xy)+(aby2+b2xy)
By taking the common factors out, we get,
=ax(bx+ay)+by(ay+bx)=(bx+ay)(ax+by)
Thus, ab(x2+y2)+xy(a2+b2)=(bx+ay)(ax+by).