欲中和B型人血清中的天然抗体，最好选用分泌型唾液为（）

A.B型

B.O型

C.任何血型

D.A型

E.AB型

—Mum, could I play with my classmates for a while after I finish my homework? 

— ________. But you must come back before supper.[ ]

A. Yes, you can

B. Yes, you could

C. No, you can't

D. No, you couldn't