火车的种类: steam train, freight train, circus train, cold train, graintrain, coal train, people-on-the-go train, bullet train 火车的部件: piston,rod,wheel 轨道的组成: steel rail,wood tie 形容词性物主代词的用法，例如: my, their 介词的用法，例如: in,on, at, over, through 连词的用法，例如: and,or 定语从句，例如: Trains have special wheels that roll on tracks 祈使句，例如: Look at some of these inventions. There be 句型，例如: There are train tracks all over the world. -般过去时的用法，例如: Robbers wanted to steal the money andgold.