At railway stations all across Britain next week, groups of students will gather with their backpacks to wait for the trains that will carry them home for Christmas. This is as large a movement of human beings as before, but with more contradictory traffic flows, so that trains filled with the young pass each other travelling in every direction. At first, I went home every weekend with my washing, but then those visits became less regular. How did I let my parents know I was coming? They had no phone. Perhaps I wrote to them ("Expect me with dirty shirts this Friday afternoon"), but more likely I didn't let them know, and just turned up or didn't turn up, not understanding that my parents' dashed hopes of seeing me were a greater casualty of my carelessness than a spoiled tea. And in all this I suspect I was typical, at least of young men. As for our fathers and mothers, none of them talked of "empty-nest syndrome", even though its implication that the principal human duty is to protect and feed the young would have suited their generation better than ours. Then, the feelings of loss went without a name. Today, it's a condition with _ , which will make parents feel more enjoyable in their life. The Mayo Clinic, for example, suggests you try to maintain regular contact with your children through "visits, phone calls, emails, texts or video chats". If you feel depressed, lean on loved ones or your mental health provider. Above all, stay positive: "Thinking about the extra time and energy you might have to devote to your marriage or personal interests after your last child leaves home might help you adapt to this major life change." What can't be denied, however, is that children often leave home. In modern societies, this is what they do. Christmas is the very time they can be depended on to return. For the non-religious, that may be this season's true comfort and significance. From the passage we can infer that by writing the article the writer's purpose is to  _  .
persuade the young to show concern for their parents ask the young to go home regularly make the young understand their parents' interests enable the young to be more independent