问题
单项选择题
主动脉瓣关闭不全，最常见的病因是（）。
A.风湿性
B.先天性
C.感染性心内膜炎
D.退行性心脏瓣膜病
E.梅毒
答案
参考答案：A
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主动脉瓣关闭不全，最常见的病因是（）。
A.风湿性
B.先天性
C.感染性心内膜炎
D.退行性心脏瓣膜病
E.梅毒
参考答案：A
几种短周期元素的原子半径及主要化合价见下表，根据表中信息，判断以下说法正确的是
| 元素符号 | X | Y | Z | R | T |
| 原子半径（nm） | 0.160 | 0.111 | 0.104 | 0.143 | 0.066 |
| 主要化合价 | +2 | +2 | -2，+4，+6 | +3 | -2 |
B．离子半径： X2+＞T2－
C．元素最高价氧化物对应的水化物的碱性：Y > R >X
D．相同条件下，等物质的量的单质与氢气化合放出能量的多少：T＞Z
I live in Hollywood. You may think people in such an attractive, fun-filled place are _________ than others. If so, you have some ________ ideas about the nature of happiness. Many intelligent people still equate(同等看待) happiness with ________. The _______ is that fun and happiness have ______ or nothing in common. Fun is what we experience during an act. Happiness is ________ we experience after an act. It is a deeper, more lasting emotion. Going to an amusement park or ball game, watching a movie or television, are fun ______ that help us relax, ________ forget our problems and maybe even ________. But they do not bring happiness, because their _______ effects end when the fun ______. I have often thought that ______ Hollywood stars have a role to ________, it is to teach us that happiness has nothing to do with fun. These rich, beautiful individuals have constant _________ to glamorous parties, fancy cars, expensive homes, everything that spells “happiness”. But celebrities reveal(揭露) the ________hidden beneath all their fun: depression, alcoholism, drug addiction, broken marriages, troubled children and profound loneliness. The way people stick to the _______ that a fun-filled, pain-free life equates happiness actually _____ their chances of ever obtaining real happiness. If fun and pleasure are equated with happiness, then pain ______ be equated with unhappiness. But, _______, the opposite is true: More times than not, things that lead to happiness _______ some pain. As a result, many people avoid the very efforts that are the source of true happiness. They fear the pain inevitably brought by such things as marriage, raising children, professional achievement, religious commitment, civic or charitable work, and self-improvement.
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