In many big cities, there are usually more than one underground line. The fastest way1 in a city is by subway. Do you know how to travel by subway?Here is some2 to know before you travel by subway. First, you should3 the right line. If you don't,you will have to get off and take4 one. Second,you need some coins(硬币)5 your ticket, because6 the machines which sell tickets only accept coins.
Coins can be changed next to the ticket machines. Or you can go to the ticket office7 some.8 you have a prepaid(预付的) card,you can just go ahead. After you have bought the9 , you should wait for your subway outside the yellow line. You10 walk too close to the yellow line. It's dangerous.
