Let X and Y have the joint p.d.f. f(x,y) = 2x²y³, 0 < x < y < 1, zero elsewhere. Find the conditional mean E(Y|X) of Y, given X = x.
A) E(Y|X) = x²
B) E(Y|X) = x³
C) E(Y|X) = x⁴
D) E(Y|X) = x⁵