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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.

1 was taken2 was accepted3 were.... stutied4 were given5 were widely applied6 was discovered7 was established8 was fond9 was attacked10 were met11 was followed12 was greatly affected13 was drawn14 were made15 was given