题干

为了解本市居民的生活成本,甲、乙、丙三名同学利用假期分别对三个社区进行了“家庭每月日常消费额”的调查.他们将调查所得到的数据分别绘制成频率分布直方图(如图所示),记甲、乙、丙所调查数据的标准差分别为s1,s2,s3,则它们的大小关系为____ (用“>”连接)

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答案(点此获取答案解析)

s1>s2>s3

同类题2

回答实验探究的相关问题.

目前,临床上癌症治疗的方法一般是先通过手术切除肿瘤,为杀死体内残留的癌细胞,在手术后进行化疗.有同学从资料上获知:二氯二乙胺能够阻止参与DNA复制的酶与DNA相互作用.由此推测:二氯二乙胺能抑制癌细胞的增殖,可作为一种癌症的化疗药物,并就此问题设计实验进行了探究.

实验材料:肝部长有肿瘤的小鼠,二氯二乙胺溶液,蒸馏水,生理盐水,含有全部营养物质的细胞培养液,显微镜,细胞计数板,试管,吸管等.

(1)下面为一学生设计的实验内容,请根据科学探究要求把实验设计补充完整.实验操作如下:

①取洁净的培养皿一个,加入适量的培养液;从小鼠肝部切取肿瘤组织并将其剪碎,利用____ 酶液处理,使细胞分散开,置于培养皿中培养.

(2)②____ .

③从培养皿中吸取等量的培养液置于各试管中,振荡后,在适宜温度下培养一段时间.

(3)④从摇匀的各支试管中吸取适量的培养液置于细胞计数板内,在低倍显微镜下观察计数板三次,记录数据如下.

实验组别

   1 

2

3

4

5

二氯二乙胺浓度(mg/mL)

   0.1   

   0.2  

   0.3  

   0.4  

    0   

细胞数目(个/mL)

计数板1

 318

271

181

89

561


计数板2

  319 

272

183

93

563


计数板3

 323

267

176

88

556

处理方法:____ 

____ 

____  

____ 

____ 

____ 

(4)根据表中所测数据,处理后在方框中用直方图直观地呈现:____ 

(5)上述细胞培养液中必需包含细胞生长的营养物质,如:____等.

(6)①在该实验中,遵循了实验设计的____ 原则和____原则.

②根据实验结果,你能得出的结论是:第一,____;第二,____ .

同类题3

根据短文理解,选择正确答案。

    LONDON—Terror struck in the heart of London on Thursday as explosions ripped through three subway trains and blasted(炸开)the roof off a crowded red double-decker bus. At least 37 people were killed and more than 700 wounded in the deadliest attack on the city since the blitz(闪电战)in World War II.

    British Prime Minister Tony Blair blamed Islamic extremists and said the bombings were designed to coincide with the opening in Scotland of a G-8 summit of the world's most powerful leaders. Foreign Secretary Jack Straw said the bombings—which came the day after London won the bid to host the 2012 Olympics--- have the “hallmarks(特点)of an al-Qaida-related attack”.

    Trapped passengers in the Underground railway threw themselves on the floor, some sobbing. As subway cars quickly filled with smoke, people used their umbrellas try to break the windows so that they could get air. Passengers emerged from the Underground covered with blood and soot(黑烟). On the street, in a light rain, buses ferried the wounded, and doctors used a hotel as a hospital.

     “I didn't hear anything, just a flash of light, people screaming, no thoughts of what it was. I just had to get out of the train,” said subway passenger Chris Randall, 28, who was hospitalized with cuts and burns to the face, the legs and hands.

     “It was chaos(混乱),” said Gary Lewis, 32, evacuated(撤离)from a subway train at King's Cross station. “The one haunting(萦绕)image was someone whose face was totally black( with soot) and pouring with blood.”

    Police said there had been no warning and that the blasts at three subway stations went off within 26 minutes, starting at 8:51 a.m. in an Underground train just outside the financial district. Authorities initially blames a power failure but realized it was a terror attack after the bus bombing near the British Museum at 9:47 a.m.—less than an hour after the first explosion.