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信号在混频时若要不产生失真，则要求信号的各频率分量在频谱搬移过程中，要保持（）和（）不变。
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Fifty years ago,zoos were places where people could go to see animals from many parts of world.The animals lived in cages that were easy to keep clean.However,for the animals,the cages were small and impossible to hide in.Although the zoo keepers took good care of them,many of the animals did not feel comfortable,and they often become ill.In modern zoos,people can see animals in more natural conditions.The animals are given more freedom in larger places so that they can live as they could in nature.In an American zoo,visitors can walk through a huge special cage that is filled with trees,some small animals and many birds.Some zoos have special places for visitors to watch animals that live in the desert or under water.Some other zoos have special places for animals that live in cold conditions like the bear from Arctic.Modern zoo not only show animals,but also keep and save rare animals,for the reason the grandchildren of today’s visitors will still be able to enjoy watching these animals. In modern zoos,（）.
SNMP的中文含义是（）
某公司2012年4月20日因水灾导致原材料发生毁损，总价值300000元，经清理，收回残料估价50000元，已入库，保险公司经查证同意赔偿200000元，款项已收存银行；其余的经批准后应计入（）账户。
BDo you often feel tired latelyHave a doctor said he can’t find anything wrong with youPerhaps he advises you to take a physical examination,but all the advanced（高级的）equipment shows that there is nothing wrong with you.Then,consider this:You might be in a state of sub-health.Sub-health,also called the third state or grey state,is explained as a borderline state between health and disease.Experts have found out that people who work in management positions as well as students around the exam-week are more likely to suffer sub-health.They may feel depressed,anxious or under stress.Sub-health symptoms（症状）are a lack of energy,depression,slow reactions and poor memory.Some other symptoms may include shortness of breath,sweating and aching in the waist and legs.According to some medical experts,the key to preventing and recovering from sub-health is to form good living habits,alternate（结合）work and rest,exercise regularly,and take part in open-air activities.As for meals,people are advised to eat less salt and sugar.They should also eat more fresh vegetables,fruit and fish because they are rich in nutrient elements that are important to the body.Experts also point out that it is not good to eat too much at one meal because it may cause unhealthy changes in the digestive（消化）system.They also say that a balanced diet is very helpful in avoiding sub-health.The last but not the least,the help and understanding of family and friends are especially important.Sometimes life can become very much difficult to cope with.Then more help may be needed. Sub-health is a kind of（）.
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