题干

已知两组数据x,x2,…,xn和y1,y2,…,yn的平均数分别为2和﹣2,则x1+3y1,x2+3y2,…,xn+3yn的平均数为(  )

A:-4

B:-2

C:0

D:2

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答案(点此获取答案解析)

A

同类题2

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

    It is impossible to know when you might find yourself lost in a forest. If you know what to do, you can survive in a forest without much trouble; but if you are not prepared, survival can be much less likely.

Keep fear at bay

    It is completely natural to be afraid when you are faced with a survival situation. ____ The more your fear overcomes you, the lower your chances are of survival, as your mind is going to become clouded and panic may set in.

Stay warm

    Obviously, the low body temperature is one of the primary dangers you face when you must survive in the forest____ Never stop to sleep or quit moving around unless you have appropriate shelter.

Know how to make a fire

    Obviously , if you have a lighter or matches, this is not a problem. But if not, you can attempt to use a dry narrow pointed stick and a dry flat piece of wood. ____ This requires a great deal of work, but if done correctly, you will succeed.

Make some shelter

    ____ The easiest way to provide protection is to find a fallen tree and cover it with other branches and brush so that you can stay in the natural pit underneath the tree trunk.This is a very important aspect of being able to survive in the forest.

Stay put unless you know exactly where you are

    If you can build a stable shelter and start a fire, you can survive in the forest for several days. ____ If you know where you are, travel as far as possible during the day while making sure you stop long enough before dark so that you can build another shelter.

A. Soon you will find that it's not that difficult to survive in the forest.

B. However, if you are going to survive in the forest, you must keep your thoughts clear.

C. Make as much friction(摩擦) as possible by rubbing the pointed stick along the flat piece.

D. It is better to stay and wait for rescue.

E. Under no circumstances should we fight with the wild animals.

F. Caves and overhangs are perfect, but most likely you must build your own.

G. It is crucial that you do all you can to stay dry and keep your body temperature up.

同类题5

中国古代是以农为本的国家,然而自宋代开始、农业中出现了“今之农与古之农异”的现象。阅读材料:

材料一:今农夫五口之家,……耕夏耘,秋获,冬藏,伐薪樵,治官府,给徭役,春不得避风尘,夏不得进暑热,秋不得避阴兩,冬不得避寒冬……。勤苦如此,尚复被水早之灾,急政暴赋,賦敛不时,朝令而幕当具。有者,半贾而卖;亡者,取倍称之息;于是有卖田宅,鬻子孙,以偿債者矣!……明主知其然也,故务民于农桑,薄赋效,广畜积,以实仓廩,备水旱,故民可得而有也。

——摘自晁错《论贵粟疏》

材料二:秋成之时,百逋丛身,解偿之余,储积无几,往往负贩佣工以谋朝夕之赢者,比比皆是也。

——(宋)王柏(鲁斋集》

材料三:一般说来,兼业的农户能比纯农业户向市场提供更丰富多样的商品,也能比纯农业户更多地从市场上购买商品,……大量兼业的农民还成为工商业经营的主体队伍中的成员。但任何事物都具有两面性、农民兼业从一开始就是与维持他们最基本的生存条件联系在一起的,个体小农在一个极低的水平上实现收支平衡,不仅减少了对纺织品、农具等一般手工业品的市场需求,而且生产出大量同类手工业品,对专业化生产构成了顽强的抵制。

——李晓《宋代工商业经济与政府干预研究》