Which of the following statements about securities exchanges is TRUE（）

A. Continuous markets are markets where trades occur 24 hours per day.

B. Call markets are markets in which the stock is only traded at specific times.

C. Setting a negotiated price to clear the market is a method that is never used in major continuous markets.

百日咳首选的抗生素是（）。

A.红霉素

B.青霉素

C.四环素

D.庆大霉素

E.氨苄青霉素