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 tiny particles or atoms and that these must be completely mixed together in the __2__. This threw a new light in the laws of definite proportions. It was __3_ necessary to suppose that the atoms could combines into small groups of uniform __5__ and so form more complex substance; thus the mystery of this law was __5__ . Dalton suggested, for example, that carbon monoxide __6__ formed by the one with one pairing of atoms of carbon and oxygen, __7_ carbon dioxide results from a single atom of carbon uniting with two atoms __8__ oxygen. Assuming this to be true, then the definite proportions of Prout′s law would naturally __9_ the relative weights of the many __10__ kinds of atoms.

1. A. gases B. pieces C. things D. gas

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

3. A. only B. too C. that D. extremely

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

5. A. solved B. discovered C. broke D. told

6. A. must B. been C. were D. is

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

8. A. from B. in C. of D. for

9. A. describe B. unit C. mix D. reveal

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

参考答案:1.A2.B3.A4.B5.A6.D7.A8.C9.B10.A