She will tell us why she feels so strongly that each of us has a role ______ in making the earth a better

place to live on. [ ]

A. to have played

B. to play

C. to be played

D. to be playing

穿心莲内酯属于（）

A．二萜类

B．二蒽酮类

C．二蒽醌类

D．双糖类

E．双黄酮类