左房室瓣关闭不全的并发症与左房室瓣狭窄的并发症相似，但前者心力衰竭情况出现较晚。

左房室瓣关闭不全的并发症较左房室瓣狭窄的并发症常见的是（）。

A.心房颤动

B.右心衰竭

C.血栓栓塞

D.急性肺水肿

E.感染性心内膜炎

B) 非选择题：阅读下列材料，然后按要求完成所给出的题目。(Read the following three passages. Each passage is followed by several questions. Respond to the questions according to the passage.)

A

Billy: I am usually very hungry by 5:30 when school is over, so I go to the nearest food shop to buy some snacks. Then I go home and do my homework. Because the workload is very heavy, I need four or even five hours to finish it. On weekends, I usually go walking in the park. There is a small mountain in the park and I often do some climbing there. That's on Sunday, but on Saturday I have to spend the day at school.

Grace: I like walking, too. I prefer going to one of the islands on weekends. During the week, like Billy, I need to deal with my lessons. But on Tuesdays I always go swimming at the local indoor pool after school. After that, I meet some friends in TV games center in Star Club. We girls like playing games as much as the boys. I go to the Internet bar to chat with some net friends on Sunday evening. I find it fantastic.

Jenny: I never go to these centers or clubs. Nearly every day I go home on time. I never chat with strangers on the Internet. I never have time for sports. I seldom watch TV at home. The only two things I do at home are studying and sleeping. After a day's work, I always feel tired. One thing I almost forget is that on Sunday evening I go to a restaurant with my parents. In a word, my life is dull and uninteresting.

Questions 51—55：Please fill in the blanks with no more than five words in each blank.