Your question is about articles, so prepositions have nothing to do with it, really, except that, as you show, the preposition, if present, would precede the article. The common patterns are: Art + Noun Art + Adj + Noun the tree, the large tree Each of these can be preceded by a preposition: Prep + Art + Noun Prep + Art + Adj + Noun with a knife with a sharp knife Under certain circumstances (related to the type of noun -- count or noncount), the article is not used: Noun Adj + Noun Prep + Noun Prep + Adj + Noun trees white flour in pain with sincerest apologies Just because they are common patterns does not make them rules, however. Hope that helps.
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