学进去

In many big cities, there are usually more than one underground line (地铁线). The fastest way to 1． in a city is by subway. How to travel by subway? Here is some 2． to know before you travel by subway. First, you should 3． the right line. If you don’t, you will have to 4． and take another one. Second, you need some coins 5． your ticket, because some of the machines which sell tickets only accept coins. 6． you have a prepaid card, you can just go ahead. After you have bought the ticket, you should wait for your subway 7． the yellow line. You must not walk too close to the yellow line. It’s 8．.