翻译练习题：
当子女外出求学或打工，父母就只能留守“空巢”，这就是所谓的空巢家庭。在一些大中城市，空巢家庭的比例在20%到30%之间，而一些小城镇的比例则高达40%。家庭结构的变迁以及敬老院的数量相对不足都是空巢老人人数增加的原因。空巢老人常要面临一系列挑战，包括调节与子女的关系，充实空闲生活，加强与外界交流，甚至还要面对他人的不理解。
参考译文：
As young people leave home for college or to start their careers, their parents are left to live on their own. These are sometimes called 'empty-nest' families. In big and middle-sized cities, empty-nest families account for 20 to 30 percent, and in small towns, the percentage is as high as 40 percent. The change in family structure, improvement in living conditions and a lack of nursing homes all contribute to the rise in number of empty nesters. Empty nest parents often face new challenges, such as establishing a new kind of relationship with their children, finding other ways to occupy their free time, reconnecting with each other, and a lack of sympathy from other people.
