巴甫洛夫所做的实验是这样的：每次给狗吃食物之前都给它一个灯光，经过灯光和食物的几次结合之后，灯光一亮，狗就要流口水。这时，灯光成了食物的信号。实验中，( )所引起的条件反射属于第一信号系统。

A．口水

B．铃声

C．食物

D．灯光

A security market in which all the bids and asks for a stock are gathered to arrive at a single price that satisfies most of the orders is best described as a:（）

A. Call market.

B. Dealer market.

C. Continuous market.