Which of the following statements regarding the expansion of (x + y)^n are correct?
A. The coefficients of x^a y^b and x^b y^a are equal.
B. For any term x^a y^b in the expansion, a + b = n.
C. For any term x^a y^b in the expansion, a- b = n
D. The coefficients of x^n and y^n both equal 1
