4．
阅读对话，根据对话内容选择正确的选项。
Sarah: Li Ming, what are you doing on the Internet? Playing games or chatting with friend?
Li Ming: Neither（都不）. I'm trying to buy three train tickets. (票)
Sarah: Where are you going?
Li Ming: I'm going back to my hometown, Sichuan. You know, it's going to be Chinese New Year next month.
Sarah: Why won't you buy the tickets next month? It's still early.
Li Ming: It is not early! Many people are going to buy tickets to go back home at the festival, but there are not so many tickets. T should buy as early as possible （尽可能）.
Sarah: Really?
Li Ming: Before the festival, China's roads, train stations and airports will be full of people. Last year, about 3, 000, 000, 000 trips were made across the country.
Sarah: So many people!
Li Ming: Yes. This is called "chunyun" in China. Some people say chunyun is the largest （最大的） annual "human migration （人类迁徒）"in the world.
Sarah: They're right. I think you'd better buy the tickets quickly.
