问题 填空题

空气是一种重要的自然资源,空气中的各种成份可以广泛用于生产和生活中.其中______约占空气体积的78%,是工业生产化肥的原料之一.人类生存不可缺少的气体是______,燃料燃烧离不开它.______虽然几乎不与其它物质发生反应,但也有广泛的用途,如制造新型电光源等.______是植物进行光和作用不可缺少的物质.(学过的填写化学式,没有学过化学式的填中文名称)

答案

空气中各成分及体积分数为:氮气:78%、氧气:21%、稀有气体:0.94%、二氧化碳0.03%、水蒸气和杂质:0.03%;

氧气的用途有:支持燃烧和供给呼吸,所以燃料燃烧离不开它;

稀有气体又叫做惰性气体,几乎不与其它物质发生反应;

植物进行光和作用的原料是二氧化碳.

故答案为:N2;O2;稀有气体;CO2

多项选择题 案例分析题
阅读理解

Whenever you send a letter or a postcard,you have to put stamps on the envelope or on the card.When did people first begin to use stamps?Who was thefirst to think of this idea?

In the early nineteenth century,people did not use stamps.They had to pay postage when they receive letters.They unhappy about this,especially whenthey pay for a letter which they did not wish to receive at a11.The postage was high at that time,because the post offices had to send many people to cotlem the postage.

RowIand Hill,a schoolnlaster in England,was the first to put forward aproposal to use stamps in the 50s of the nineteenth century.fie thought it wouldbe much easier for people to use stamps to coover postage.They could go to the nearby post office to buy stamps and put them on envelopes before they sent theletters,The post office simply put seals on the stamps so that people could notuse the staraps again.In this way,the post office did not need to send postmen tocollect postage.It only needed to send fewer postmen to deliver letters.’That was a good idea and the governmern finally accepted it.

小题1:It was not until that people began to use stamps.

A.!he early 19th Century    B.the middle 19th century

C.the late 19th century    I).the beginning of the 19th century

小题2:Before stamps were used,postage    

A.was paid by the letter—posters

B.was paid by the letter—receivers

C.was collected by postmen

D.BothBand C小题3:After stamps were used,post offices needn’t        

A.send postmen to collect the postage

B.send postmen to collect letters

C.send postmen to deliver jetters

D.put seals on the used stamps小题4:Which of the following may be the best title of the passage?

A.When did people first begin to use stamps?

B.Who was the first to think of using stamps?

C.Why were postmen sent to collect postage?

D.How did stamps come Into use?