在正八边形中，与所有边均不平行的对角线有______条．

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答案

正八边形的对角线条数=

×8×（8-3）=20，

又∵正八边形的对角线中有8条平行与边的对角线，

∴在正八边形中，与所有边均不平行的对角线有12条．

故答案为：12．

单项选择题

1 Millions of teens are on weight-reducing diets. Although maintaining a healthy body weight is important, obsessive dieting can lead to eating disorders. Eating disorders can disrupt lives and sometimes even result in death.
Starving Oneself
2 Anorexia nervosa is an eating disorder in which people starve themselves. Anorexics have an irrational fear of becoming fat and see themselves as much heavier than they really are. They shun food and may exercise for hours every day in an attempt to lose weight.
3 Female anorexics may never mature sexually or may stop menstruating because they lose too much body fat, causing the level of sex hormones to fall. Their body temperature and pulse rate become abnormally low; their hair becomes thin and dry; and their resistance to infection drops.
Bingeing and Purging
4 Patients with bulimia engage in frequent episodes of bingeing (eating a large amount of food in a short time). After a binge, they almost always purge by self-induced vomiting or by using laxatives. Therefore, their weight stays fairly constant. Unlike anorexic patients, bulimics often recognize that their behavior is abnormal and often feel guilty, depressed, and helpless.
5 The frequent purging removes salts from the body, which can eventually lead to muscle weakness, heart failure, and kidney disease. The vomiting gradually destroys tooth enamel and results in unhealthy gums.
Help for People with Eating Disorders
6 Little is known about what causes anorexia nervosa and bulimia. Many people believe that western society’s emphasis on thinness in women is largely to blame. However, recent research suggests that genetic factors might also be involved. Both eating disorders can be managed with a combination of medical treatment, counseling, and family support.

What may be the influence of anorexia on female

A．muscle weakness and heart failure

B．kidney disease and low body temperature and pulse rate

C．dropping resistance to infection

D．destroyed tooth enamel and unhealthy gums

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单项选择题 A1/A2型题

肾综合征出血热典型的临床特征是（）

A.发热、出血、腓肠肌疼痛

B.发热、出血、皮疹

C.发热、出血、休克、肾损害

D.发热、出血、昏迷

E.发热、出血、休克、肝损害

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