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【C1】______must exist in the form. of 【C2】______particles or atoms and that these【C3】______be completely mixed together in the【C4】______. This threw a new light in【C5】______laws of definite proportions. It was 【C6】______necessary to suppose that the atoms【C7】______combine into small groups of uniform【C8】______and so form. more complex substance;【C9】______the mystery of this law was【C10】______. Dalton suggested, for example, that carbon monoxide【C11】______formed by the one with one【C12】______of atoms of carbon and oxygen,【C13】______carbon dioxide results from a single【C14】______of carbon uniting with two atoms【C15】______oxygen. Assuming this to be true,【C16】______the definite proportions of Prout' s law (【C17】______all chemical compounds the different constituents【C18】______enter in unvarying proportions) would naturally【C19】______the relative weights of the many【C20】______kinds of atoms.
【C1】

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