Which of the following is NOT a rule of omission of articles? 

In some circumstances, we can omit the article without changing the sentence's structure or meaning. Before the names of people, places, months, and specific countries, there should be no article. Before the names of the metals, no articles should be used. Language names should not be preceded by any articles. Before the abstract nouns, do not use any articles. Any article should not come before proper nouns. When used in its broadest sense, no article should be used before common nouns. Before the names of the months and the days of the week, articles must be omitted. No articles should come before plural nouns; hence option c is the correct answer because articles can be used before singular nouns.