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数据库三级模式中，可以存在“多个“的模式是哪个？
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视频中提到了哪些主流的数据库系统？
视频中提到，1970年诞生了直到目前为止最重要、最主流的一类数据库，他是：
If you’re looking for ways to improve your products or services, customers can be one of your most valuable sources of information and market research（研究）, so why not take it a step further and visit some of them?Ideally, you want to do this in person, so you may need to offer your customers something for their time. They may be pleased that you take their opinion seriously, and they may also enjoy getting a chance to help influence your products or services, If your customers are in different places, you could make such visits part of your business travel to get a wider range of responses.One expert recommends（建议）that you make your customers feel comfortable during the visits. You’re not trying to sell anything through these meetings, so plan to spend 80 percent of your time listening.Don’t try to lead your customer to give responses that you really want to hear. Instead, ask questions that focus on the customer’s experience such as whether they got what they were hoping for and what they found difficult or enjoyable.1. According to the passage, your customers can be very helpful in____.A. expanding your businessB. reducing your production costC. selling your products or servicesD. improving your products or services2. In the first paragraph, the author suggested _____ .A. paying a visit to some customersB. finding out sources of informationC. advertising your products or servicesD. carrying out various market researches3. Your customers may feel happy if you ______.A. take them as your good friendsB. treat their opinions seriouslyC. offer quick responsesD. visit them regularly4. According to the expert, the way to make your customers comfortable during the visit is_______.A. to promise them the best priceB. to explain your sales plan to themC. to spend most of your time listeningD. to tell them the advantages of your products5. The focus of your questions during the visit should be on_________.A. the development of your businessB. responses that you want to hearC. the customer’s experienceD. your future sales plan
Task2If you do not use your arm or your legs for some time, they become weak; when you start using them again, they slowly become strong again. Everybody knows that. Yet many people do not seem to know that memory （记忆力） works in the same way. When someone says that he has a good memory, he really means that he keeps his memory in practice by using it. When someone else says that his memory is poor, he really means that he does not give it enough chance to become strong. If a friend says that his arms and legs are weak, we know that it is his own fault (过错). But if he tells us that he has a poor memory, many of us think that his parents are to blame (受责备), and few of us know that it is just his own fault. Have you ever found that some people can't read or write but usually they have better memories? This is because they cannot read or write and they have to remember things; they cannot write down in a little notebook. They have to remember days, names, songs and stories; so their memory is the whole time being exercised. So if you want to have a good memory, learn from the people: Practice remembering.6. The main reason for one is poor memory is that ________.A. his father or mother may have a poor memoryB. He does not use his name or legs for some timeC. his memory is not often usedD. he can’t read or write7. If you do not use your arms or legs for some time ________.A. you can't use them any moreB. they will become strongerC. they become weak and won't become strong until you use them again.D. they will become neither stronger nor weaker8. Which of the following is NOT true?A. Your memory works in the same way as your arms or legs.B. A good memory comes from more practice.C. A good memory comes from practising more.D. Don't learn how to read and write if you want to have a better memory.9. Some people can't read or write, but they usually have better memories, because ________.A. they have save much troubleB. they have saved much time to remember thingsC. they have to use their memories all the timeD. they can’t write everything in a little notebook10. Which is the best title for this passage?A. Don't Stop Using Your Arms Or LegsB. How To Have a Good MemoryC. Strong Arms And Good MemoriesD. Learn From the People
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