药物的特异性作用机制不包括（）

A.激动或拮抗受体

B.影响离子通道

C.改变细胞周围环境的理化性质

D.影响自身活性物质

E.影响神经递质或激素分泌

A bond is needed when the bill of lading cannot be availed of the time of entry of the im- ported commodities. What does the sentence mean.（）

A. A bond is needed when the bill of lading is unavailable when the goods arrive at the destination.

B. A bond is needed when the bill of lading arrives at the port of destination.

C. A bond is not needed when the goods arrive at the destination.

D. A bond is needed when the goods arrive at the destination if there is no bill of lading at all.