Definition: You are given a question on college mathematics. You are also given 4 answer options (associated with "A", "B", "C", "D"), out of which only one is correct. You need to answer the question by selecting the correct option. You should only answer with the choice letter, not the whole answer.
Input: Let f(x,y) = x^2 - 2xy + y^3 for all real x and y. Which of the following is true?
(A)f has all of its relative extrema on the line x = y. (B)f has all of its relative extrema on the parabola x = y^2. (C)f has a relative minimum at (0, 0). (D)f has an absolute minimum at (2/3, 2/3).

A