部屋が暗いから、電気を___ください。 (The room is dark, so please turn on the light.)

Answer and explanation

Correct answer: D. つけて

電気をつける is transitive; 電気がつく is intransitive.
Answer: つけて.
Why not the others: ついて: つく is intransitive and does not take を. つける: ください needs the て-form. つけない: that would say do not turn it on.

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