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