Dalton wondered why the heavier and lighter gases in the atmosphere did not separate as oil and water do.He finally concluded that the constituent 1 must exist in the form of 2 particles or atoms and that these 3 be completely mixed together in the 4 .This threw a new light in 5 laws of definite proportions.It was 6 necessary to suppose that the atoms 7 combinesintossmall groups of uniform 8 and so form more complex substance; 9 the mystery of this law was 10 .Dalton suggested, for example, that carbon monoxide 11 formed bythe one with one 12 of atoms of carbon and oxygen, 13 carbon dioxide results from a single 14 of carbon uniting with two atoms 15 oxygen.Assuming this to be true, 16 the definite proportions of Prout's law (17 all chemical compounds the different constituents 18 enter in unvarying proportions) would naturally 19 the relative weights of the many 20 kinds of atoms.

　　1.A.gases B.pieces C.things D.gas

　　2.A.timely B.trimmed C.tiny D.topical

　　3.A.ought B.could C.will D.must

　　4.A.sky B.atmosphere C.oxygen D.environment

　　5.A.various B.many C.the D.those

　　6.A.only B.too C.that D.extremely

　　7.A.should B.were C.get D.could

　　8.A.construct B.structure C.piece D.feature

　　9.A.but B.also C.thus D.nevertheless

　　10.A.solved B.discovered C.broked D.told

　　11.A.must B.been C.were D.is

　　12.A.putting B.pairing C.placing D.preparing

　　13.A.while B.when C.therefore D.also

　　14.A.piece B.type C.atom D.measure

　　15.A.from B.in C.of D.for

　　16.A.then B.so C.by D.that

　　17.A.from B.in C.to D.for

　　18.A.are B.wouldn’t C.always D.never

　　19.A.describe B.unit C.mix D.reveal

　　20.A.different B.usual C.important D.chemical

　　1.【答案】A 根據(jù)上文中的heavier and lighter gases可以確定,本空中應(yīng)填入“組成的氣體”，即constituent gases。

　　2.【答案】C 根據(jù)句子意思判斷,句中的詞意為微粒的意思，選項(xiàng)C.tiny合乎題意。

　　3.【答案】D 情態(tài)動(dòng)詞must在這里是“必定、必須”的意思。

　　4.【答案】B sky意為“天空”，atmosphere意為“大氣”, oxygen意為“氧氣”, environment意為“環(huán)境”,只有B項(xiàng)正確。

　　5.【答案】C 這幫助解釋了大氣組成氣體的比例確定原理。因?yàn)槭翘刂高@一原理，用定冠詞the。

　　6.【答案】A only necessary的意思是“僅僅是必要”。故A正確。

　　7.【答案】D 根據(jù)句子意思判斷, could是“能夠”的意思。

　　8.【答案】B 根據(jù)句子意思判斷,這里需要“結(jié)構(gòu)”這個(gè)詞，而B合乎題意。

　　9.【答案】C but，nevertheless表示轉(zhuǎn)折意為“但是”，“然而”;thus意為“因此”，如There has been no rain.Thus, the crops are likely to suffer.一直沒有下雨，因此莊稼可能會(huì)受害。這里與上文有因果關(guān)系，故應(yīng)選C。

　　10.【答案】A solve相當(dāng)于find a solution or an answer to,意為“解決”、“解開”,如: solve a problem (a puzzle, a mystery);discover相當(dāng)于find something existing but not known before,意為“發(fā)現(xiàn)”,如: discover a place (a fact, the truth)。因此應(yīng)選A。

　　11.【答案】D 因?yàn)槭潜硪话阋?guī)律，又是單數(shù)，所以用is這個(gè)詞。

　　12.【答案】B Pair這里是“匹配，配成雙”的意思。

　　13.【答案】A while表示對(duì)比。如：Some substances are soluble, while others are not.一些物質(zhì)是可溶的，而另一些物質(zhì)是不可溶的。

　　14.【答案】C 根據(jù)句子意思判斷, atom正確。

　　15.【答案】C of表示“含量，分量”。

　　16.【答案】A then的意思是next, after that。

　　17.【答案】D for的意思是“對(duì)于，就……而言”。

　　18.【答案】C 根據(jù)句子意思判斷。

　　19.【答案】B describe意為“描述”;unite意為“結(jié)合，合并”;mix意為“(不同的東西)混合在一起”，如：mix flour and water;reveal意為“揭露，揭示”。

　　20.【答案】A 根據(jù)句子意思判斷.