their

1. DET You use their to indicate that something belongs or relates to the group of people, animals, or things that you are talking about. 他们的; 她们的; 它们的

Janis and Kurt have announced their engagement. 贾尼斯和库尔特已宣布订婚。

2. DET You use their instead of "his or her" to indicate that something belongs or relates to a person without saying whether that person is a man or a woman. Some people think this use is incorrect. 用于代替“他的”或 “她的”，不指明是男是女

Each student determines their own pace in the yoga class. 每个学生决定他们自己在这个瑜珈班的学习速度。