题干

下列关于生物实验方法的描述正确的是(  )

A:观察细胞中的染色体数目,实验材料为紫色洋葱鳞片叶外表皮细胞

B:在纸层析法分离叶绿体中色素的实验结果中,滤纸条上蓝绿色的色素带最宽,原因是叶绿素a在层析液中溶解度最高

C:观察植物细胞的减数分裂,不可选用开放的豌豆花的花药作为实验材料

D:探究促进生根的最适NAA浓度需要做预实验,其目的是减小实验误差

上一题 下一题 0.0难度 选择题 更新时间:2019-09-11 07:32:46

答案(点此获取答案解析)

C

同类题1

阅读理解

    Experts say that, among young Internet users, it's not boys who create most web content. The pioneers of the Internet at the moment are the girls.

    According to Jenny Baker, whose hobbies are designing icons(图示), most boys just aren't patient enough for blogging, uploading photographs, and creating their own websites. Jenny posts her pictures on her own website, and believes that most boys don't often have their own sites. She thinks it's mainly girls.

    And Jenny is right. A study shows that, among Internet users aged 12 to 17, a lot more girls blog than boys (35 percent of girls compared with 20 percent of boys). A lot more girls also work on their web pages (32 percent of girls compared with 22 percent of boys). Girls are also ahead of boys in working on websites for other people.

    Some girls have their own teenage podcasts(播客)which have become very successful and sometimes the creators have their own TV shows too. When asked what they think about the study that shows girls are more active on the web, they say that they're not surprised because girls are very creative, and sometimes more creative than boys.

    Other girl have started interactive(交流的)e-zines with articles written for girls by girls. “Girls from everywhere read our articles, and they ask lots of questions,” they say. “I think girls like to help other people more.” One expert said: “If boys were more interested in helping other people, the numbers would be different.”

    But if girls are more interested in computers, why do women only have 27 percent of computer-related jobs? Maybe this will change in the future—after all, girls like these will be in the job market before too long.

同类题5

根据短文理解,回答下列问题。

    The Internet is becoming more and more important in our life. How much do you know about it? What is the Internet? The Internet is a large, worldwide collection of computer networks. A network is a small group of computers put together. The Internet is many different networks from (A)                 the world. These networks are called the Internet. Once you have learned to use the Internet, you can have a lot of interest in the World Wide Web.

    What is the World Wide Web?

    The World Wide Web has been the most popular development of the Internet. The Web is like a big electronic book with millions of pages. These pages are called homepages. You can find information about almost anything in the world on these pages. For example, (B) you can use the Internet instead of a library to find information for your homework. You can also find information about your favourite sports or film stars, talk to your friends or even do some shopping on the Internet. Most pages have words, pictures and even sound or music.

    What is e-mail? (C)电子邮件是给别人发送信息的一种方法。 It's much quicker and cheaper than sending a letter. If you want to send e-mails, you must have an e-mail address. This address must have letters and dots(点 ) and an ‘@’( meaning ‘at'). This is what an address looks like: Emily @ star. net. Write a message, type in the person's e-mail address, and then send the message on the Internet. People don't need to use stamps, envelopes or go to the post office since the invention of the Internet. Quick. easy and interesting--that's the Internet!