In the proof showing that if n is an odd integer, then n^2 is odd, why does the solution assume n to be 2k + 1?
A) The assumption simplifies the algebraic manipulation required in the proof.
B) It is a common property of odd integers that they can be expressed as 2k + 1.
C) The assumption is arbitrary and does not affect the validity of the proof.
D) The assumption ensures that n^2 is divisible by 2k, making it an odd integer.