A call market is least likely characterized as a market:（）

A. with bid-ask prices posted by dealers.

B. where buy-sell orders are cleared at a single equilibrium price.

C. with participation by a small number of active investors-traders.

药物作用是（）

A.药物使机体细胞兴奋

B.药物与机体细胞间的初始作用

C.药物与机体细胞结合

D.药物引起机体功能或形态变化

E.药物使机体细胞产生效应