He delayed writing the book until he had done a lot of research. Only when……….……………………………………........................?

Tạm dịch: Anh ấy trì hoãn việc viết cuốn sách cho đến khi anh ấy đã tìm tòi rất nhiều.
Ta có cấu trúc đảo ngữ: Only when + S + V + trợ động từ + S + V: Chỉ khi … thì …
→ Đáp án: Only when he had done a lot of research did he write/ begin/ startwriting/ to write the book.
Notes:
- research /rɪˈsɜːrtʃ/ (n) sự nghiên cứu
→ do research (v) làm nghiên cứu
- start/begin + to V/V-ing (v) bắt đầu làm gì
- delay = postpone + Ving: trì hoãn

He delayed writing the book until he had done a lot of research. Only when……….……………………………………....................................

He delayed writing the book until he had done a lot of research.
Only when……….……………………………………....................................