質問: Most people use いろいろ質問する. But if I analyze it, いろいろ is な形容詞. So I think it should be いろいろな質問する. What do you think?
回答: いろいろ can also be considered an adverb. If you are describing the **types** of questions, いろいろな質問 would be correct. But in the case of いろいろ質問する, you are talking about the **action** of asking different things, and thus doesn't require な.