Correct Answer: D
Explanation:
DO
(brother of) → REY
(sister of) → MI
(brother of) → FA
Either I or II could be true, but not both. We know that Do, Rey, Mi and Fa are all siblings (since Do is Rey’s brother, Rey is Mi’s sister, and Mi is Fa’s brother). But we do not know Fa’s sex. If Fa is a girl, I is true. If Fa is a boy, II is true. So either I or II could be true, but not both at the same time.