题干

命题“∀n∈N*,f(n)∈N*且f(n)≤n”的否定形式是(  )

A:∀n∈N*,f(n)∉N*且f(n)>n  

B:∀n∈N*,f(n)∉N*或f(n)>n

C:∃n0∈N*,f(n0)∉N*且f(n0)>n0

D:∃n0∈N*,f(n0)∉N*或f(n0)>n0

上一题 下一题 0.0难度 选择题 更新时间:2016-11-24 06:04:02

答案(点此获取答案解析)

D

同类题4

阅读下文,回答问题

只想和你接近

    在我十六岁离家之前,我们一家七口全睡在同一张床上——那种把木扳架高,铺着草席,冬天加上一层垫被的通铺。

    这样的一家人应该很亲近吧?没错。不过,不包括父亲在内。

    父亲可能一直在摸索、尝试与孩子们亲近的方式,但老是不得其门。同样的,孩子们也是。

    小时候特别喜欢父亲上小夜班的那几天,因为下课回来时他不在家。因为他不在,所以整个家就少了莫名的肃杀和压力,妈妈准确地形容是“猫不在,老鼠呛秋”。

    午夜父亲回来,他必须把睡得横七竖八的孩子一个个搬动、摆正之后,才有自己可以躺下来的空间。

    那时候我通常是醒着的。早就被他开门闩门的声音吵醒的我通常装睡,等着洗完澡的父亲上床。

    他会稍微站定观察一阵,有时候甚至会喃喃自语地说:“实在啊睡成这样!”然后床板会轻轻抖动,接着闻到他身上柠檬香皂的气味慢慢靠近,感觉他的大手穿过我的肩胛和大腿,整个人被他抱起来放到应有的位子上,然后拉过被子帮我盖好。

    喜欢父亲上小夜班,其实喜欢的仿佛是这个特别的时刻——半分钟不到,却是完全满足的亲近。

    长大后的某一天,我跟弟弟妹妹坦承这种装睡的经历,没想到他们都说:“我也是!我也是!”

    或许亲近的机会不多,所以某些记忆特别深刻。

    有一年父亲的腿被落盘压伤,伤势严重到必须从矿工医院转到台北的一家外科医院治疗。 由子住院的时间很长,妈妈得打工养家,所以他在医院的情形几乎没人知道。某个星期六的中午我放学之后,不知道是什么样的冲动,我竟然跳上开往台北的火车,下车后从火车站不停地问路走到那家外科医院,然后在挤满六张病床和陪伴家属的病房里,看到一个毫无威严、落魄不堪的父亲。

    他是睡着的,四点多的阳光斜斜地落在他消瘦不少的脸上。他的头发没有梳理,既长且乱,胡子也好像几天没刮的样子;打着石膏的右腿露在棉被外,脚指甲又长又脏。

    不知道为什么!我想到的第一件事竟然就是帮他剪指甲。护士说没有指甲剪,不过可以借给我一把小剪刀;然后我就在众人的注视下,低着头,忍住一直冒出来的眼泪,小心地帮父亲剪指甲。

    当我剪完所有的指甲,抬起头才发现,父亲不知道什么时候已经睁着眼睛看着我。 “妈妈叫你来的?”“不是。”“你自己跑来没跟妈妈说?”“没有。”

    直到天慢慢转暗,外头霓虹灯逐渐亮起来之后,父亲才开口说:“暗了,我带你去看电影,你晚上就睡这边吧!”

    那天夜晚,父亲一手撑着我的肩膀,一手拄着拐杖,小心穿越周末熙攘的人群,走过长长的街道,带我去看了一场电影。

    一路上,当我不禁想起小时候和父亲以及一群叔叔伯伯,踏着月色去九份看电影的情形时,父亲正好问我:“记不记得小时候我带你去九份看电影?”

    那是我人生第一次一个人到台北,第一次单独和父亲睡在一起,第一次帮父亲剪指甲,却也是最后一次和父亲一起看电影。

    那是一家比九份升平戏院大很多的电影院,叫远东戏院。那天上演的是一部日本片,导

    演是市川昆,片名叫“东京世运会”。

    片子很长,长到父亲过世二十年后的现在,它还不时在我脑海里上演着。

(吴念真/文,有删改。)

同类题5

阅读理解

    A day in the life of 18-year-old David Lanster is full if typical teenage stuff: school, baseball practice and homework. And then he starts cooking. “Some nights I'm up until 1:00 a.m. making pies, or even later if we're cooking beef,” said the student at Ransom Everglades High School in Florida, US.

    For the past year, Lanster and Kelly Moran, his classmate, have been hosting fancy dinner parties at Lanster's parents' home. Their meals have 17 courses and are all made by them. Their guests used to give them gifts to thank them until the pair decided to do something nice for charity(慈善). “We got some really great Miami Heat tickets, a nice watch, and many kitchen gadgets(小器具),” Lanster said. “But we wanted to make this something positive for people other than us.”

    Lanster and Moran focused on Common Threads, a charity that aims to teach kids in poor communities to cook and make healthy eating choices. The young cooks ask their guests to give however much they want as payment for their meals. It all goes to Common Threads because Lanster's parents cover their food costs. After their last 12-person event, Lanster and Moran gave $1,600 to the charity.

    Now, they're taking their show out of the kitchen and on the road. They have started to organize private dinner parties with a similar model: the host pays for the ingredients, and the guests make a donation to a charity of their choice.

    Without formal training, Lanster said he had been interested in cooking since he helped his mom in the kitchen when he was very young. He learned how to cook by reading cookbooks and watching TV programs. Outside the kitchen, the two are busy preparing their college applications. Neither of them is sure what they will do in the future, but they're promised their parents that they will leave professional cooking alone until they finish school.