The main thing which this passage reveals about Sinclair's intention is to:
This refers to the type of essay in which a person writes to expose a social problem that has been previously unknown to educate the public.
With this in mind, we can note that Sinclair Upton wrote the book The Jungle as a form of expository essay to show the unhygienic practises which were taking place in the meat packing industry.
Therefore, the correct answer is option D
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