题干

如果随机变量ξ~N(μ,σ2),且Eξ=3,Dξ=1,则P(-1<ξ≤1)等于(    )

A:2Φ(1)-1

B:Φ(4)-Φ(2)

C:Φ(2)-Φ(4)

D:Φ(-4)-Φ(-2)

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D

同类题1

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    Palema Malhotra and her husband Anil Malhotra have spent the last 25 years buying the waste agricultural land and reforesting it, to return the land to a bio – diverse rainforest for elephants, birds and other creatures.

    The couple owns 300 acres of land in Brahmagiri, India. They have spotted more than 300 kinds of birds as well as many rare and threatened animal species. But, this was not the scene in 1991 when Anil and Pamela came to this part of the country. “When I came here, it was a wasteland. The owner wanted to sell because he couldn't grow coffee or anything else,” says Anil who worked in the real estate(房地产)and restaurant business in the US before moving to India. “For me and Pamela, this was what we were looking for all our life.”

    The couple had a love for nature from their childhood. When the Malhotras came to India, the pollution horrified them. “That was when we decided to do something to reclaim(开垦)the forest in India,” says Anil. “We were not looking for money. Early on, we realized that shortage of fresh water will be a concern for India and the rest of the world. Acquisition, protection and reclamation of forested lands and wildlife habitat, where vital water sources have their origin, is the only way to save ourselves,” explains Anil.

    They sold what they owned in America, bought the first 55 acres and began to grow a forest. Soon they bought the land nearby as well. “Many of the farmers considered their holdings 'wasteland' as very little grew on it and were happy to get money,” says Anil.

    Hunting and poaching(偷猎)was a challenge and often the locals did not understand what this couple was doing, so it required a lot of talking to create awareness. They worked with the forest department to set up camera traps and keep poachers away. “There are times I have fought with poachers,” says Pamela.

同类题4

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月夜

       喧嚣的校园在晚休的铃声中渐渐沉睡了,宿舍里同学们的欢闹声,已经听不见了;偶尔听到的只是远处池塘里的几声蛙鸣。在这幽微的月光里,毕业离校的幽苦又萦上心头,我鬼使神差地走到校园后面的林荫小道上。

       曲曲折折的小径,蔓草横生。不知名的白色野花挨挨挤挤地开着,像是一地银白的精灵,在月光里摇曳婆娑。两旁的玉兰树,是我们来时栽下的,现在已蓊蓊郁郁,两人多高了。月华如洗,透过扶疏的叶隙,撒下一地的斑驳。

       我想起了第一学期和同学们一起度过的那个中秋月夜。马鞍山上,芝山亭中,在满月的光里,大家欢聚一堂,品茗、吃月饼,畅谈理想、人生,遐想着月的传说。月光皎洁,马鞍山披着一层银辉。风儿带着秋的凉意,沙沙地响过了竹林,响过了芝山亭。记得苏子有言:江上之清风,与山间之明月,耳得之而为声,目遇之易成色,取之无禁,用之不竭,是造物者之无尽藏也,而吾与子之所共适。那时我想,我们真是一群幸运的人儿,搭在世纪末人才的班车上,享受着太平盛世的风光霁月,展望着未来岁月。

       又是一个月夜。因白天一位同学病了,我带他去看病,一时没请假,旷了半天课。班主任周老师叫我去她家一趟。我想,坏了,要挨批了。我忐忑不安地蹭进了老师的家。

       以后有事要记得先请个假。他身体好些了吗?接着,周老师又说,他家挺困难的,这些钱你捎给他,就说是他家里寄的。

       你们是同乡,他不会怀疑,我明天上完课再过去看他我买了几帖中药

       我无言,捏着这张带有体温的50元钱,望着老师纤弱秀丽的背影,我平生头一回体味到了一种山的威严。走出老师的家,我蓦地发现,今晚的月好圆好圆

       重温往事,同学情使我感到甜蜜,师生情更使我感到温暖。在这离别的时刻,双眸不由湿湿的。在微微的泪光中,我又看到了窗口那盏熟悉的灯还亮着,那是老师在辛勤地工作吗?这样想着,不觉已回到宿舍。均匀的鼻息声微微响着,舍友们已睡熟好久了。