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周期性功率信号的自相关函数和互为傅里叶变换关系。

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互相关函数反映两个信号的相关程度，它和无关，只和有关。

列宁对辩证唯物主义物质范畴的定义是通过主体和客体的关系来界定的。

A. 对
B. 错

Directions :Read the texts from a magazine section called“Letters”in which five people wrote about on-line shopping. For questions 36 -40, match the name of each person to one of the statements(A-G) given below. Mark your answers on your ANSWER SHEET.Jennifer:In your article about online shopping being the newest and easiest way to shop, you said thatcomputers will replace shopping malls sooner or later because they make buying things faster andcheaper. But don' t you think that the entire point of shopping is to spend leisure time with friendswhile doing something necessary. Shopping is not just a quick task. It is, in fact, an entire way oflife.Paul:I am a great collector of all manner of hard-to-find items such as out-of-print books and antiques. Purchasing in physical stores would mean round-the- world travel and years of effort. I can get the same result in a few hours on eBay, and often at bargain prices. I am quite well-off, butbuy very few consumer items available in regular shops. I have many friends and acquaintances with the same approach.Mike:My wife buys online often. I have not heard complaints or dissatisfaction. She can compare with different online vendors' prices after she has decided what she wants. It' s delivered to the door, a big time savings and gas savings. If I need something, I check online first and see what it costs and then decide where to buy, local stores or online. Online has the advantage most of the time.Henry:Virtually all online stores make you register. But, I don't need another usermame and pass word to remember. I will only buy online if I cannot find something locally. Even though shipping is fast, I' d rather drive across town and pay more to be able to bring home a new gadget the same day. And, most of the time, there is no difference in price between local stores and online stores.Jeff:If you think the prices are the same online as they are locally, you' re dealing with the wrong online retailers. I' m an online shopping veteran and I always save quite a bit on my large-dollar purchases. With a little research experience, I've easily saved thousands of dollars over the last several years. Besides, shipping on most items is reasonable and you don't even pay taxes 99.9% of the time.Now match the name of each person (36- 40) to the appropriate statement.Note: there are two extra statements.Statements36. Jennifer[ A] I'll buy online only when I have to.37. Paul[B] You can enjoy steep discounts with most online sellers.38. Mike[C] I do buying on or off line depending on what suits me.39. Henry[D] Shopping is not only a necessary task but a sociable pleasure.40. Jeff[ E] Online selling helps to satisfy my special needs in buying.[F] Buying online is far from being as good as it is boasted to be.[G] Buying online can save you a lot only if you find the right online sellers.

Directions: Read the texts from a magazine article in which five people talk about tipping in a restaurant. For questions 36 -40, match the name of each person to one of the statements (A- G) given below. Mark your answers on your ANSWER SHEET.Richard:I've always viewed tipping as a way of saying“thank you" to the one who serves me. I believe what is bad is when no tip is left at all. The better the service, the higher the tip. Unless the service is literally perfect, I never tip more than l0% of the bill. Much like the harder teachers in school, I never give an easy“ A.”My assessment is honest.Daniel:A tip is a “thank you,” but in truth，a tip is payment for service. 20% is a standard tip. Servers deserve it for their hard work. Restaurants will never pay more for labor unless they are forced to do so by new laws. Tips make up about 97% of a server' s total income. Those tips are needed for survival. So, before servers are paid a living wage," tip 20% .Kate:Why should I pay the difference between what the restaurant is willing to pay the employee and what an acceptable wage is? I do pay 20% , but I hate it. A friend of mine left Europe for New York City, found a job in a restaurant there and ended up making $ 5 ,500 a month. Enough above minimum wage? How about miners , construction workers ; resident doctors, etc? Do they get tipped?Patricia:18 - 20% for good service is today' s standard. The restaurant and its employees are too polite to tell you this or to put it on their menus, but that is their expectation and you need to understand that. I believe it is good manners to respect this. To do otherwise is to be openly rude. If you disagree, you are wise to eat elsewhere, as you are hurting a hardworking professional.Michael:Tipping has gotten out of control. I always had thought it was 15%，and now suddenly servers have made it 20%. I tip 15% , and that' s it. If the service is really superior, then I work higher from there. Interesting to be told, “If you can' t afford to tip 20%，then you should eat at home.” If all those people stayed away, the restaurant would not even be in business.Now match the name of each person (36 -40) to the appropriate statement.Note: there are two extra statements.Statements36. Richard[ A] It's not polite not to tip.37. Daniel[ B] I do tip, though I don't like it.38. Kate[ C] Tipping shouldn't be compulsory.39. Patricia[ D ] Tips are essential to servers’ survival.40. Michael[ E] If you don't tip, you are punishing the server.[ F] I think tipping standard today is too high.[ G] Better service means higher tips.