Answers:
1.We had been playing tennis for about an hour when it started to rain heavily.Explanation: "Had been playing" (past perfect continuous) is used to describe an action that was ongoing in the past up until another action occurred.
Dịch: Chúng tôi đã chơi tennis được khoảng một giờ khi trời bắt đầu mưa lớn.

2.I was very tired when I got home. I had been working hard all day.Explanation: "Had been working" (past perfect continuous) shows an ongoing action in the past before another event (I got home).
Dịch: Tôi rất mệt khi về nhà. Tôi đã làm việc chăm chỉ cả ngày.

3.At last the bus came. He had been waiting for 20 minutes.Explanation: "Had been waiting" (past perfect continuous) indicates the duration of waiting before the bus arrived.
Dịch: Cuối cùng chiếc xe buýt cũng đến. Anh ấy đã chờ đợi 20 phút.

4.Jim quit drinking coffee two years ago. He had been drinking coffee for 20 years.Explanation: "Had been drinking" (past perfect continuous) shows a habit or action that continued up until a specific point in the past.
Dịch: Jim đã bỏ uống cà phê cách đây hai năm. Anh ấy đã uống cà phê suốt 20 năm.

5.She was out of breath. She had been running.Explanation: "Had been running" (past perfect continuous) explains the cause of her being out of breath.
Dịch: Cô ấy thở hổn hển. Cô ấy đã chạy.

6.It wasn't raining when we went out. The sun was shining. But it had been raining, so the ground was wet.Explanation: "Had been raining" (past perfect continuous) is used to describe a prior event that left a visible result (the ground was wet).
Dịch: Trời không mưa khi chúng tôi ra ngoài. Mặt trời đang chiếu sáng. Nhưng trời đã mưa trước đó, vì vậy mặt đất bị ướt.