化简:2(x2y+xy)-3(x2y-xy)-4x2y.

题型:解答题

问题:

化简:2(x2y+xy)-3(x2y-xy)-4x2y.

考点:整式的加减
题型:解答题
列式或列方程计算.
(1)一个数的50%比30少6,求这个数.
(2)27的
5
9
是一个数的
1
3
,求这个数.
题型:解答题

典型心绞痛患者含服硝酸甘油后,疼痛应在多长时间内缓解()

A.几秒钟内

B.1~5分钟

C.10~15分钟

D.20分钟左右

E.30分钟以上

题型:解答题
In the past, man did not have to think about the protection of his environment. There were few people on the earth, and natural resources seemed to be____36____ .
Today things are___37_____, the world has become too___38____ . We are using up our natural resources too quickly, and at the same time we are___39____ our environment with dangerous chemicals. If we continue to do this, human life on the earth ___40____survive.
Everyone___41_____ today that if too many fish are taken from the sea, there will soon be none left. Yet, with modern fishing__42_____ , more and more fish are caught. We know that if too many trees are cut down, ___43____will disappear and nothing will grow on the land. Yet, we ___44_____to use bigger and more powerful machines to __45____more and more trees.
We realize that if rivers are polluted with waste products from factories, we will die.___46_____, in most countries wastes are ___47______put into rivers or into the sea, and there are _48_____laws to stop this.
We know, too, that if the___49____ of the world continues to rise at the present rate, in a few years, there will not be enough___50_____. What can we do to solve these problems ?
It we eat more vegetables and less___51____, there will be more food available for everyone. Land that is used to grow crops __52_____five times more people than land where animals are kept.
Our natural resources will _53_____longer if we learn to recycle them. The world population will not rise so quickly if people use modern methods of birth__54_______ .
Finally, if we educate people to think about the problems, we shall have a better and clearer ___55____in the future.
小题1:
A.beautifulB.unlimitedC.rareD.valuable
小题2:
A.commonB.the sameC.changeableD.different
小题3:
A.crowdedB.smallC.dirtyD.busy
小题4:
A.protectingB.savingC.pollutingD.fighting
小题5:
A.may notB.will notC.shall notD.could not
小题6:
A.wondersB.realizesC.considerD.discovers
小题7:
A.polesB.boatsC.methodsD.ideas
小题8:
A.mountainsB.the seaC.treesD.forests
小题9:
A.continueB.haveC.oughtD.will go on
小题10:
A.growB.plantC.saveD.cut down
小题11:
A.ThusB.HoweverC.Generally speakingD.Therefore
小题12:
A.stillB.evenC.alsoD.certainly
小题13:
A.too manyB.a fewC.someD.few
小题14:
A.productionB.pollutionC.populationD.revolution
小题15:
A.housesB.vegetablesC.foodD.lives
小题16:
A.fruitB.meatC.fishD.grain
小题17:
A.feedsB.increasesC.suppliesD.helps
小题18:
A.useB.stayC.keepD.last
小题19:
A.controlB.bornC.planD.reward
小题20:
A.natureB.seaC.planetD.Forest
题型:解答题

为什么不锈钢的含铬必须大于13%?

题型:解答题

单层钢结构主体结构的整体垂直度允许偏差为H/1000,且不应大于()。

A.-25.0

B.+25.0

C.±25.0

D.25.0

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