--- They have never seen the film,         they?

--- Yes, they have.

A．have

B．haven’t

C．do

D．don’t

甲型强心苷C₁₇连接的不饱和内酯环是（）

A.五元不饱和内酯环

B.五元饱和内酯环

C.六元不饱和内酯环

D.六元饱和内酯环

E.七元不饱和内酯环