Each year in the United States more people are killed or injured in accidents—at home, at work or school, at play, or while traveling—than were killed or injured in the Vietnam war. In the early 1990s, about half of these accidental deaths were the result of motor-vehicle accidents. Other major causes of accidental deaths were falls, fires, and poisoning. On a worldwide basis, accidents involving motor vehicles are the primary cause of accidental deaths, followed by accidents in industry and in the home.
Efforts to lessen or to eliminate the hazardous conditions that cause accidents are known as safety measures. Safety is a growing concern around the world, and safety skills fire being taken more seriously today than ever before People have Come to realize that safety skills can be learned, and most safety experts agree that it is possible to predict, and take steps to prevent, the majority of accidents. Few accidents simply "happen". Most are caused by ignorance, carelessness, neglect, or lack of skill.

单纯二尖瓣狭窄时，下列说法不正确的是（）

A.第一心音亢进是因为左心室收缩功能降低

B.可引起声嘶

C.不会引起左心室扩大

D.最早期症状为劳累性呼吸困难

E.可出现右心衰