腰部

例句：

1. 1. He sat on the couch with his back against the wall.
   他坐在沙发上，背靠着墙。
2. 2. She stretched her arms out to reach for the ball.
   她伸展双臂去够那个球。
3. 3. The doctor advised him to exercise regularly to maintain a healthy back.
   医生建议他定期锻炼以保持健康的背部。