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: Plasma cells are activated B cells that secrete antibodies., Fact2: Antibodies are produced by plasma cells., Question: antibodies are produced by activated B cells that do what? (A) Animal survival (B) killing insects (C) interact (D) secrete them (E) migrate (F) reproduce (G) competition (H) Allergies
D