题干

若数列an满足规律:a1>a2<a3>...<a2n-1>a2n<...,则称数列an为余弦数列,现将1,2,3,4,5排列成一个余弦数列的排法种数为(    )

A:12

B:14

C:16

D:18

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答案(点此获取答案解析)

C

同类题2

阅读下面的文言文,完成小题。

    胡世宁,字永清,仁和人。弘治六年进士。性刚直,不畏强御,且知兵。除德安推官。岐王初就藩,从官骄,世宁裁之。

    迁广西太平知府。太平知州李浚数杀掠吏民,世宁密檄龙英、知州赵元瑶擒之。母丧归。服阕赴京。道沧州,流寇攻城急,世宁即驰入城,画防守计。贼攻七日夜,不能拔,引去。

    迁江西副使。当是时,宁王宸濠骄横有异志,莫敢言,世宁愤甚。正德九年三月上疏日:“敕王止治其国,毋挠有司,以靖乱源,销意外变。”宸濠闻,大怒。列世宁罪,遍赂权幸,必杀世宁。世宁已迁福建按察使取道还里宸濠遂诬世宁逃驰使令浙江巡按潘鹏执送江西鹏尽系世宁家人索之急。李承勋为按察使,保护之。世宁乃亡命抵京师,自投锦衣狱.

    狱中三上书言宸濠逆状,卒不省。系岁余,言官程启充、徐文华、萧鸣凤、邢寰等交章救,乃谪戍沈阳。居四年,宸濠果反。世宁起戍中为湖广按察使。寻擢右佥都御史,巡抚四川。以父忧归。

    世宁风格峻整,居官廉。疾恶若仇,而荐达贤士如不及。都御史马昊、陈九畴坐累废;副使施儒、杨必进考察被黜;御史李润、副使范辂为时所抑,连章荐之。与人语,呐不出口,及具疏,援据古今,洞中窾会。与李承勋善,而持议不苟合。始以议礼与张璁、桂萼合,璁、萼德之,欲援以自助,世宁不肯附会,论事多牴牾。诸大臣皆忌之。帝始终优礼不替。

    九年秋卒。赠少保,谥端敏。

摘编自《明史·列传第八十七》

同类题5

根据短文理解,选择正确答案。

    "The first of June, and the King family is going on holiday tomorrow! " said Meg. "I'm free for three months!"

    "And Aunt March went away for her holiday today." said Jo. "Isn't life wonderful!"

    "What will you do all your holiday?" asked Amy.

    "I'll stay in bed late, and do nothing." said Meg.

    "I have lots of books to read." said Jo.

    "Let's not do any studying, Beth...." said Amy. "Let's play all the time and rest, as Jo and Meg are going to do."

    "I will if Mother doesn't mind." said Beth.

    Mrs. March agreed to the plan and said they could try it for a week.

   "But," she added, "I think by Saturday night you will find that all play and no work is as bad as all work and no play."

    Next day, Meg appeared at ten o'clock and ate breakfast alone. It was a lonely meal and the room was untidy, because Beth had not cleaned it.

    Jo went to the river with Laurie, then sat in the apple tree and read a book. Beth began to tidy things in her cupboard, but she got tired and left it half-done. She went to her piano, glad that she did not have to wash the cups and plates. Amy sat in the garden to draw, hoping someone would see her and say something nice about her picture. But no one appeared, so she went for a walk, got caught in the rain and came home very wet.

    At tea, everyone said that it had been a happy but unusually long day. Meg, who had been shopping in the afternoon, now decided that she did not like the dress she had bought. Jo had a headache from reading too long. Beth couldn't find anything in her cupboard, and the rain had made Amy's dress so wet that she couldn't wear it to Katy Brown's party the next day.

    Mrs. March listened, smiled and said nothing.

    The week seemed to get longer and longer with nothing much to do, and by Friday the girls were glad that it was nearly over. Then Mrs. March gave Hannah a holiday, and when the girls got up on Saturday, there was no breakfast ready, no fire in the kitchen, and no mother waiting for them.

    "What has happened?" said Jo.

    Meg ran upstairs, then came down to say that Mother was staying in her room to have a rest.

    "She says we must look after ourselves today." Meg said.

    "Good, I want something to do." said Jo.

    Secretly, they were all pleased to have something useful to do again. Beth and Amy put cups and plates on the table while Jo and Meg got the breakfast, then Meg took some tea and an egg up to Mrs. March. The tea was too strong and the egg was burned. Mrs. March did not complain, but she laughed to herself afterwards.