When I arrived, they (have) dinner.

Phương pháp làm:
1. Xác định thì của động từ "have" trong câu: dựa vào "arrived" có thể suy ra đây là hành động xảy ra trước khi "I" đến, vì vậy ta dùng thì quá khứ hoàn thành (past perfect).
2. Đặt câu hỏi theo dạng "Have they had dinner?"
3. Trả lời:
- Yes, they had had dinner when I arrived.
- No, they hadn't had dinner when I arrived.

Hoặc

- Yes, they had dinner when I arrived.
- No, they didn't have dinner when I arrived.

When I arrived, they were about to have dinner.

When I arrived, they had just finished dinner.

When I arrived, they were having dinner.

When I arrived, they had already had dinner.