完形填空

　High school students in America hear about twenty bells 　1　 . The first bell is the tardy bell (上课铃). If students are not in their seats when the tardy bell　　 　2　　 　, they know they are late. 　3　　 　bell rings at the end of 　4　　 　class, and everyone　　 　5　　 　class quickly and goes to 　6 　. When students are in 　7　　 　class, they are often happy to hear the bell ring;but if the class is interesting; they do not want the bell 　8 　. Most students like the lunch bell best. They know that it is time 　9　　 　their friends for lunch. They buy a hot meal in the school dining-room or they bring their lunch from home in a big paper bag.

　After a nice lunch everybody knows　　 　10 　it is soon time for another bell, another bell, another bell...