题干

如图,用K、A1、A2三类不同的元件连接成一个系统.当K正常工作且A1、A2至少有一个正常工作时,系统正常工作,已知K、A1、A2正常工作的概率依次是0.9、0.8、0.8,则系统正常工作的概率为(   )

A:0.960

B:0.864

C:0.720

D:0.576

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答案(点此获取答案解析)

B

同类题4

阅读理解

    Herbal medicine (草药), which has been used for medicinal purposes, is the use of plants to treat diseases. Many herbalists use the entire plant, from the flowers, stems, leaves, and roots, in the form of everything from teas to pills. These plants contain natural, chemical things that can treat the body for a variety of diseases- such as allergies, asthma, rheumatoid arthritis, migraine, chronic fatigue, and cancer, among others.

    Nowadays an increasing number of people prefer to adopt these plants to treat their diseases because, compared with chemical medicine, herbal medicine has its own advantages. Herbal medicine and remedies (治疗) are more effective than chemical medicine for certain diseases. The chemical medicine given by a chemist could have certain negative side effects. However, many of the herbal medicine and remedies do not have negative side effects. If any, they are softer than chemical medicine. Obesity is the cause of many of the health problems. Herbal medicine can help weight-loss more effectively and improve overall health.

    However, the cure using herbal medicine and supplements (营养品) would take some time, and therefore people are supposed to possess enough patience. Worse still, herbal medicine contains a variety of ingredients (成分) and people have to be sure that their body agrees with the ingredients and that it is not allergic (过敏).

    A point worth mentioning here is herbal remedies and medicine for certain illnesses may have negative side effects. These side effects may not be shown at once, but would take months or even years. In the early stages, if the herbal medicine is not agreeing with you, it is wise to stop using it.

    When used correctly and directed by doctors, herbs can help treat a variety of diseases. But keep in mind that the herbal medicine industry is not regulated, so herbal products are often misleading and may contain additives (添加剂) and that are not listed on the label (标签). Some herbs may cause allergic reactions or interact with other drugs, and some are poisonous if used improperly or at high doses (剂量). Taking herbs on your own increases your risk.

同类题5

阅读下面的作品,完成后面小题。

“这是你的战争!”

宗璞

    ①昆明下着雪。红土地、灰校舍和那不落叶的树木,都蒙上了一层白色。几个学生从明仑大学校门走出,不顾雪花飘扬,停下来看着墙上的标语:“这是你的战争!This is your war!”

    ②前几天,学校举行了征调动员大会。盟军为中国抗战提供了大批新式武器和作战人员,由于言语不通,急需译员。教育部决定征调四年级男生入伍,其他年级的也可以志愿参加。

    ③历史系教授孟弗之从校门走出,他刚上完课。无论时局怎么紧张,教学必须坚持到最后一刻。一起走的几个学生问:“做志愿者有条件吗?”弗之微笑答道:“首先是爱国热情。英语也要有一定水平,我想一个大学生的英语水平足够对付了。”他看着周围的年轻人。谁将是志愿者?他不知道。可是他知道那些挺直的身躯里跳动着年轻的火热的心。

    ④弗之走了一段路,迎面走来几个学生,恭敬地鞠躬。“孟先生,我们是工学院三年级的,愿意参加翻译工作。”弗之想说几句嘉奖的话,却觉得话语都很一般,只亲切地看着他们年轻而带几分稚气的脸庞,乱蓬蓬的黑发上撒着雪花,雪水沿着鬓角流下来,便递过一块叠得方整的手帕。一个学生接过,擦了雪水,又递给另一个,还给弗之时已是一块湿布了。

    ⑤雪越下越大了。弗之把那块湿布顶在头上,快步往回走。这时,一个年轻人快步跟上来,绕到前面,唤了一声:“孟先生。”弗之认得这人,中文系的,似乎姓蒋。他小有才名,文章写得不错,能诗能酒,也能书能画。“孟先生。”那学生嗫嚅着又唤了一声。弗之站住,温和地问:“有什么事?”蒋姓学生口齿不清地说:“现在四年级学生全部征调做翻译,我……我……”弗之猜道:“你是四年级?”“我的英文不好,不能胜任翻译。并且我还有很多创作计划……”“无一例外。”弗之冷冷地说,并不看他,大步走了。蒋姓学生看着弗之的背影,忽然大声说:“你们先生自己不去,让别人的子弟去送死!”弗之站住了,一股怒气在胸中涨开,他回头看那学生。学生上前一步:“只说孟先生是最识才的,叫人失望。”弗之转身,尽量平静地说:“你,你无论怎样多才,做人是不能打折扣的,一切照规定办。”弗之走得很慢,自觉脚步沉重,回到住处时,只见院子里腊梅林一片雪白。

    ⑥此刻,弗之的外甥、生物系学生澹台玮正在萧子蔚老师的房间里。玮是三年级,但学分已够四年级。师生两人对坐在小木桌旁,讨论着生物学的问题。子蔚感到玮有些心不在焉,已有点猜到他的心思。待讨论告一段落,玮说:“萧先生,我要做的事是要和您说的。”子蔚微笑道:“不是商量,是通知?”玮道:“也是商量。”他停顿了一下,说:“我只觉得战场和敌人越来越近,科学变得远了,要安心念书似乎很难。”“可是你并不在征调之列。生物化学是新学科,需要人开拓,要知道得到一个好学生是多么不容易。我也很矛盾。”子蔚站起身,走到窗前。雪已停了,腊梅林上的雪已消了大半。玮也走到窗前,默默地望着窗外。过了一会儿,玮转身向着子蔚:“我会回来的。”“那是当然。”子蔚说。玮向子蔚鞠了一躬。子蔚向前一步,拉着他的手郑重地说:“我尊重你的决定。”玮再鞠一躬,走出房间,回头说:“萧先生,我去了。”子蔚默默地看着他下楼,又到窗前,看他出了楼门,沿小路往腊梅林中去了。

(节选自长篇小说《西征记》,有删改,标题为选者所拟。)