There were so many cars held up by the heavy rain on the road that we had no        but to wait.  [      ]

A. alternative        

B. difference        

C. relation            

D. opposition

请说出防风的来源、主产地、药用部位、主要成分、鉴别特征及功效。

防风的主要成分有（）

A.生物碱类

B.黄酮类

C.挥发油

D.蒽醌类

E.皂苷类

F.香豆素类