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Put the verbs into passive forms:
1. The most important step____(take) when Mendeleyev studied the relation between
die atomic weights and the properties of the elcmcnts.2. The periodic law____(accept)
and widely used by chemists. 3. Properties of chemical elements and compounds
(thoroughly study) in laboratories.4. Some elements _____(give) hew places in the
table after the revision of their' atomic weights. 5. The periodic lavs ____(widely
apply) by.6. Radon (discover) during the investigation of the properties of
radium and radioactive substances. 6. An important role of oxygen in combustion____(discover) by Priestley. 7. The modem concept of combustion_____(establish) by Lavoisier. 8. Oxygen____(find) in the free state
in the atmosphere.9, When a substance_____(attack) by oxygen, it forms an oxide or
a number of oxides. 10 Many kinds of oxides_____(meet) with in the study of chemistry
11. The lecture_____(follow) by the demonstration of experiments. 12. The yield of
the reaction_____(greatly affect) by temperature. 13. Attention ___(draw) to the valence of substances. 14. Attempts _____(make) to obtain pure
oxygen. 15. Much attention____(give) recently to the study of this group of oxides.