An analyst does research about tradingsessions. Which of the following statements is most accurate to describe the characteristics of a call market（）

A. Dealers who provide securities liquidity engage in proprietary trading.

B. Gathering all trades to the same place at the same time makes it easier for buyers to find sellers and vice versa.

C. A willing buyer and seller can trade at anytime the market is open.

可用性或称即需性，是指导保证商业信息及时获得和保证服务不被拒绝（）