Given the task definition and input, reply with output. In this task, you are given two facts, and a multiple-choice question. Based on the given facts, answer the question with index of the correct option (e.g, "A").

Fact1: Courtship is behavior that is intended to attract a mate., Fact2: Birds sing to defend territories and attract mates., Question: How do birds court and defend territories? (A) Summer (B) sound (C) ligt (D) singing (E) mechanical (F) movement (G) exercise (H) autumn
D