题目

下图是某反应的微观示意图。 请回答：  (1)B框中的物质属于___(填序号)。 ①化合物 ②单质 ③纯净物 ④混合物 (2)此反应的化学方程式为____，此图说明化学反应前后发生改变的微粒是__ __。 答案：②③_2H2S＋3O22SO2＋2H2O分子 阅读理解 　　The Internet has led to a huge increase in credit-card(信用卡)fraud．Your card information could even be for sale in an illegal web site(非法网站)． 　　Web sites offering cheap goods and services should be regarded with care． 　　On-line shoppers who enter their credit-card information may never receive the goods they thought they bought．The thieves then go shopping with your card number-or sell the information over the Internet．Computers hackers(黑客)have broken down security(安全)systems, raising questions about the safety of cardholder information．Several months ago, 25,000 customers of CD Universe, an on-line music retailer(零售商), were not lucky．Their names, addresses and credit-card numbers were posted on a Web site after the retailer refused to pay US ＄157,828 to get back the information． 　　Credit-card firms are now fighting against on-line fraud．Mastercard is working on plans for Web-only credit card, with a lower credit limit．The card could be used only for shopping on-line．However, there are a few simple steps you can take to keep from being cheated(欺骗)． 　　Ask about your credit-card firm's on-line rules：Under British law, cardholders have to pay the first US ＄78 of any fraudulent(欺骗性的)spending． 　　And shop only at secure sites; Send your credit-card information only if the Web site offers advanced secure system． 　　If the security is in place, a letter will appear in the bottom right-hand corner of your screen．The Web site address may also start https：//-the extra“s”stands for secure．If in doubt, give your credit-card information over the telephone． 　　Keep your password(密码)safe：Most on-line sites require a user name and password before placing an order．Treat your passwords with care． (1) What is the meaning of“fraud”? [　　] A． Cheating． B． Sale． C． Payment． D． Safety． (2) How can the thieves get the information of the credit card? [　　] A． The customers give them the information． B． The thieves steal the information from Web sites． C． The customers sell the information to them． D． The thieves buy the information from credit card firms． (3) How many pieces of advice does the passage give to you? [　　] A． Four． B． Three． C． Five． D． Six． (4) You are shopping on the site：http：//www.Shopping.com, and you want to buy a TV set, what does this article suggest to do? [　　] A． Order the TV set at once． B． Do not buy the TV set on this site． C． E-mail the site your credit-card information． D． Tell the site your password and buy the TV set for you．