Rewrite the sentence: He delayed writing the book until he had done a lot of research. Only ..............

Only after/ when he had done a lot of research did he (begin to) write the book.

Dịch: Chỉ sau / khi anh ấy đã nghiên cứu rất nhiều, anh ấy mới (bắt đầu) viết cuốn sách.