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.

阻塞性睡眠呼吸暂停低通气综合征常见的狭窄和阻塞的部位是

A．鼻和鼻咽

B．气管和支气管

C．口咽和软腭

D．舌根部

E．喉咽部