A. a            B. an                C. the                 D. /

(   ) 13.Mother dogs have several babies _______.

A. on a time     B. in a time           C. at any time           D. at a time

(   ) 14. Some people kill tigers and make medicine _______ their bones.

A. from             B. of                    C. into                  D. out

(   ) 15. —I'm sorry to keep you waiting here so long.

—_______.

A. Don't do that again, please.                B. Well, I'd love to wait.

C. You're welcome to say th at.                D. Oh, not at all.