💡 Detailed Explanation
The grammar pattern '〜ことにする' (koto ni suru) is used when the speaker makes a personal decision or determination (to decide to do / to make it a rule to). Sentence translation: 'I have decided not to smoke starting tomorrow.' Because it represents a personal decision, the subject must be the speaker (or the person who made the decision, typically 'I'). Option 2 is incorrect because we cannot decide the actions of our teacher. Option 3 is incorrect because we cannot decide natural phenomena like rain. Option 4 is incorrect because state/properties ('old') cannot be 'decided' using this pattern.