💡 Detailed Explanation
The correct choice is 'なれ' (from '慣れる' - to get used to / adapt). Combined with 'だんだん' (gradually), '慣れました' perfectly describes the process of adapting to a new country. Sentence translation: 'Half a year has passed since I came to Japan, and I've gradually gotten used to life here.' 'あき' (to get tired/bored of), 'つかれ' (to get tired/fatigued), and 'おどろき' (to be surprised) do not represent this positive adaptation process.