question: Hint: Please answer the question and provide the correct option letter, e.g., A, B, C, D, at the end.
  Question: When does the function reach its local maximum?
  Choices:
  (A) (u1, u2) = (0, 0)
  (B) (u1, u2) = (1, 0)
  (C) (u1, u2) = (0, 1)
  (D) (u1, u2) = (1, 1)