Sociology is study of society. Population Explosion is one of the social issues. Many other issues we come across in our daily lives are social issues. Therefore, it is understood that the given passage talks about some social issue for which one may or may not mention the word 'sociology' in the title. However, even if it is not included it doesn't make the title bad due to the fact which is understood that we are talking w.r.t social context. There may not be any fixed title to the passage or there may be as many titles as the no. of candidates!

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