Сделать! put the verbs into passive forms: 1. the most important ) when mendeleyev studied the relation between die atomic weights and the properties of the elcmcnts.2. the periodic ) and widely used by chemists. 3. properties of chemical elements and compounds (thoroughly study) in laboratories.4. some elements ) hew places in the table after the revision of their' atomic weights. 5. the periodic lavs apply) by.6. radon (discover) during the investigation of the properties of radium and radioactive substances. 6. an important role of oxygen in ) by priestley. 7. the modem concept of ) by lavoisier. 8. ) in the free state in the atmosphere.9, when a ) by oxygen, it forms an oxide or a number of oxides. 10 many kinds of ) with in the study of chemistry 11. the ) by the demonstration of experiments. 12. the yield of the affect) by temperature. 13. attention ) to the valence of substances. 14. attempts ) to obtain pure oxygen. 15. much ) recently to the study of this group of oxides.

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