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: Lymphocytes are the key cells involved in the immune response., Fact2: An allergy attack is an immunal response., Question: What are the key cells in an allergy attack? (A) layers of fat (B) Lymphocytes. (C) fur and fat (D) bone cells (E) muscle cells (F) the skin (G) Red blood cells (H) animals
B