问题 选择题

下列物质的鉴别方法正确的是

A.氮气和氧气——闻气味

B.二氧化锰和木炭——观察颜色

C.碳酸钙和硫酸铜——观察能否溶于水

D.氢气和一氧化碳——点燃后观察火焰颜色

答案

答案:C

题目分析:依据物质的性质,采用物理或化学方法加以鉴别,要求能够有明显的不同现象。

A、氮气和氧气都是没有气味的气体,故用闻气味的方法,无法区别,错误;

B、MnO2和木炭都是黑色固体,因此用观察颜色的方法不能鉴别,错误;

C、碳酸钙不溶于水,硫酸铜能溶于水,且溶液为蓝色,故可加水观察其能否溶于水来鉴别,正确;

D、氢气和一氧化碳都具有可燃性,且火焰都为淡蓝色,故不可用点燃后观察火焰颜色来区分,错误。故选C

点评:理解和熟练掌握常见物质的性质,是解题的关键;注意鉴别物质时,一定要有不同的明显现象,才可以正确区分。

问答题

注意:下面出现的“考生文件夹”均为c:\wexam\25160001。 (1) 在考生文件夹下有工程文件sjt3.vbp及窗体文件sjt3.frm,该程序是不完整的,请在有号的地方填入正确内容,然后删除及所有注释符(即’号),但不能修改其他部分。存盘时不得改变文件名和文件夹。如图17-3所示。 本题描述如下: 在窗体上有一个标签数组,名为Label1,该数组有4个控件元素,标题分别是“程序运行”、“文本编辑”、“双向箭头”和“移动窗体”。在程序运行后,将鼠标移动到各控件元素上,则鼠标的形状将变成各控件元素的标题所代表的鼠标形状,离开控件元素,则又变成正常情况下的箭头形状。 (2) 在考生文件夹下有工程文件sjt4.vbp,窗体文件sjt4.frm,该程序是不完整的,请在有号的地方填入正确内容,然后删除及所有注释符(即’号),但不能修改其他部分。修改后的工程及窗体文件,均以原名保存在考生文件夹下。如图17-4所示。 本题描述如下: 在窗体上有一个名为Text1的文本框,有两个命令按钮,名称分别是C1和C2,标题分别是“读入”和“计算并保存”。要求程序运行后,点击C1按钮,将文本文件in6.txt中的所有数字读到数组arr中,并在文本框内显示出来。随后C1按钮变为无效;然后点击C2按钮,求出数组arr中的各元素的平方并赋值回相应的元素,例如,arr(2)=2,则令arr(2)=arr(2)*arr(2)=4。把计算后的数组的值全部写入考生文件夹下的文本文件out6.txt中,并在文本框中显示出来,最后C2按钮也变为无效。

单项选择题

People don’t want to buy information online. Why Because they don’t have to. No more than that because they’re used to not paying for it. That’s the conventional wisdom. Slate, Microsoft’s online politics-and-culture magazine, is an oft-cited example of the failed attempts to charge a fee for access to content. So far, for most publishers, it hasn’t worked.

But nothing on the Web is a done deal. In September graphics-soft-ware powerhouse Adobe announced new applications that integrate commerce into downloading books and articles online, with Simon & Schuster, Barnes and Noble, and Salon. corn among its high-profile partners. Some analysts put the market for digitized publishing at more than $100 billion. Of course, if the Internet can generate that kind of money—some might say almost any kind of money—people want in. And this couldn’t come at a better time. Newspaper and magazine writers in particular are increasingly frustrated by their publishers, which post their writings online but frequently don’t pay them extra.

So here’s the good news: Fathrain. com, the third biggest book-seller on the Net—after Amazon. com and Barnesandnoble. corn—is now doing just what the publishing industry that made it a success fears., it’s offering a secure way to pay for downloadable manuscripts online. Fatbrain calls it offshoot eMatter. With it, the company’s executives have the radical notion of ousting publishers from the book-selling business altogether by giving writers 50% of each and every sale (To reel in authors, eMatter is running a 100% royalty promotion until the end of the year. ) Suggested prices to consumers range from a minimum $ 2 to $ 20, depending on the size of the book to download.

"This will change publishing forever!" Chris MaeAskill, co-founder and chief executive of Fatbrain, declares with the bravado of an interior decorator. "With eBay, anybody could sell antiques. Now anybody can be published. "

There’s been no shortage of authors wanting in. Within a few weeks, according to the company, some 2,000 writers signed on to publish their works. Some of this is technical stuff—Fatbrain got where it is by specializing in technical books—but there are some well-known writers like Catherine Lanigan, author of Romancing the Stone, who has put her out-of-print books and a new novella on the site. Another popular draw is Richard Bach, who agreed to post a 23-page short story to the site.

Not everyone thinks downloadable documents are the biggest thing in publishing since Oprah’s Book Club. "I think it will appeal to sellers more than buyers," says Michael May, a digitalcommerce analyst at Jupiter Communications, which released a report that cast doubt on the market’s potential. "A lot of people are going to publish gibberish. The challenge is to ensure the quality of the work. "

Blaine Mathieu, an analyst at Gartner Group’s Dataquest, says, "Most people who want digital content want it immediately, I don’t know if this model would satisfy their immediate need. Even authors may not find that Web distribution of their works is going to bring them a pot of gold. For one thing, it could undermine sales rather than enhance them. For another, anybody could e-mail downloaded copies of manuscripts around town or around the world over the Net without the writer’s ever seeing a proverbial dime. " Softlock. com, Authentica and Fatbrain are trying to head this problem off by developing encryption padlocks that would allow only one hard drive to receive and print the manuscripts. For now, the problem persists.

According to the passage, the author implies that people don’t have to buy information on Net because()

A. it’s always free to download information from websites

B. most writers offer free copies on Net

C. publishing companies offer free copies on Net

D. anybody can e-mail downloaded copies