A：酶、雄性激素、抗体
B：胰岛素、抗体、生长激素
C：雄性激素、载体、酶
D：维生素、甲状腺激素、雌性激素
— Come and join us, Ben!— I'm afraid I can't. I'm too busy now. If I ________ time, I would certainly go.
