2. 外语
  3. Dalton wondered why the heavier and lighter gases in the atmosphere did not separate as oil and water do. He finally concluded t

Dalton wondered why the heavier and lighter gases in the atmosphere did not separate as oil and water do. He finally concluded t

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问题    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 of atoms and that these【C3】______be completely mixed together in the【C4】______.
   This threw a new light on【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 substances;【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 toms【C15】______oxygen. Assuming this to be true,【C16】______the definite proportions of Proust’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.
【C18】
选项 A、are
B、couldn’t
C、always
D、never
答案C
解析 enter in动词短语，应用副词修饰，本句子需表肯定意义的副词，故排除never，选择always。
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