why when how
In big cities,many people take buses,trains or subways to get from one place to another.Buses are a popular means of transportation.If you are using a bus,you need to know which bus to take and where you can get on.You also need to be able to  read the timetable right,so you can take the right bus and get to your place on time.At last,you need to know [MASK] to get off and tell the driver the name of the station.