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当前学科：经济学
题目：
单选题
当总效用增加时，边际效用应该（）。
A
为正值，且不断增加
B
为正值，但不断减少
C
为负值，且不断减少
D
为正值可能增加也可能减少。
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活动挡烟垂壁联动调试的检查方法不包括（）。
Camping Camping wild is a wonderful way to experience the natural world and， at its best， it makes little environmental influence. But with increasing numbers of people wanting to escape into the wilderness， it is becoming more and more important to camp unobtrusively （不引人注目地） and leave no mark. Wild camping is not permitted in many places， particularly in crowded lowland Britain. Wherever you are， find out about organizations responsible for managing wild spaces， and contact them to find out their policy on camping and shelter building. For example， it is fine to camp wild in remote parts of Scotland， but in England you must ask the landowner's permission， except in national parks. Camping is about having relaxation， sleeping outdoors， experiencing bad weather， and making do without modern conveniences. A busy， fully-equipped campsite （野营地） seems to go against this， so seek out smaller， more remote places with easy access to open spaces and perhaps beaches. Better still， find a campsite with no road access： walking in makes a real adventure. Finding the right spot to camp is the first step to guaranteeing a good night's sleep. Choose a campsite with privacy and minimum influence on others and the environment. Try to use an area where people have obviously camped before rather than creating a new spot. When camping in woodland， a void standing dead trees， which may fall on a windy night. Avoid animal runs and caves， and possible homes of biting insects. Make sure you have most protection on the windward side. If you make a fire， do so downwind of your shelter， always consider what influence you might have on the natural world. Avoid damaging plants. A good campsite is found， not made — changing it should be unnecessary. ometimes you need to make electricity.（）
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