题目

如图，在多面体ABCDEF中，AB＝2EF，EF∥AB，，H为BC的中点． 求证：FH∥平面EDB. 答案：设AC与BD交于点G，联结EG、GH. 则G为AC中点，∵H是BC中点，∴GH綊AB 又∵EF綊AB， ∴四边形EFHG为平行四边形． ∴FH∥EG. 又EG⊂平面EDB，而FH⊄平面EDB， ∴FH∥平面EDB.Every year many students went to the college bookstore to purchase the different textbooks that they need for their classes. Little do these students realize that, in doing so, they are throwing good money away. It may sound unbelievable but textbooks, in some cases, actually cost as much as, if not more than, college fees.Many people think that college bookstores are the most convenient source for textbooks. Titles are usually kept and students may purchase new textbooks or choose to buy second-hand books and save money. But the money saved by purchasing second-hand textbooks from college bookstores is small compared to the amount they could save by shopping online.More and more online booksellers have begun selling textbooks at heavily discounted prices. Online second-hand bookstores are another source for college books as they keep a large number of textbooks, which means sizable savings for students. Students should avoid purchasing their textbooks at the first store that they surf online since there are so many ‘unreal’ booksellers on the Net. Price isn't the only factor to consider when making an online purchase. Students should also consider shopping costs and delivery time when making their decision.Online auctions(拍卖) are another option for students seeking a bargain. This option, however, has its pros and cons. A plus is that students can get incredibly cheap books. One problem is that while online bookstores have a system in place that ensure you receive your order within a reasonable amount of time, with an auction purchase, however, you  must depend on the auction seller's timetable. One way that students can really save is by getting books for free. Project Gutenberg is one resource that English majors will find invaluable. Here students can legally download a huge collection of classic novels. In the past students needing help with their studies would often have to spend a lot of money buying expensive study guides. Today that is no longer the case. Cash-strapped students can now visit the website SparkNotes for free downloadable study guides as well as classics1.Which of the following is the best title of this passage?A.Learning to Save on TextbooksB.Why Buy TextbooksC.Online ShoppingD.Tips for Buying Secondhand Textbooks2.Which of the following is NOT mentioned as a source to obtain textbooks ?A.College bookstoresB.Online used bookstoresC.Online auctionsD.Second-hand bookstore centres3.The underlined expression “pros and cons” (paragraph 4) is closest in meaning to _______.A.professionals and conservativesB.joy and sadnessC.advantages and disadvantagesD.processes and conditions4.According to the passage, Project Gutenberg is probably _______.A.a government project aimed at helping English majorsB.a project to help poor students get free learning materialsC.a website for English majors to get the guides from language expertsD.a website for students to get free sources for English learning5.From the passage, we can learn that_______.A.the cost of textbooks in college is low compared to the amount spent on tuitionB.online auctions are perfect for students seeking text booksC.students should visit many websites before buying their booksD.students should consider shopping costs and delivery time above all else when making their buying decision