We were visiting an old building. They were going to a traditional market. (while)
→ We were visiting an old building while they were going to a traditional market.
(Mình thấy để while lên trước vẫn đúng mà sao sách giải phải bắt buộc bỏ while ra vế sau vậy ạ)
Giaỉ thích chi tiết giúp mình