通常情况下，一个外中断服务程序的第一条指令是STI，其目的是( )。A．开放所有屏

     Several days ago, some students from the US visited our school. When we talked, I discovered __1__
differences in school life between the US and China. For example, each class __2__ fifty minutes in the
US. It is a little __3__ than that in China. We usually have forty of forty-five minutes in each class. Another
difference is that they have less break time between __4__. Besides, although (虽然) most schools in both
countries finish their __5__ classes at 12 o'clock, the students in the US only have an hour-long break, so
they __6__eat lunch quickly. Their afternoon classes begin at 1: 00 p.m. and school is over __7__ 3 : 00
p.m.  Then they take part in club activities or play sports.
     Many Chinese students don't work during their high school years, while the US students like to find a
part-time job in __8__ free time. They don't have a dream job in mind. They think __9__ is no difference
between jobs. Working is a useful experience for them and they can make money at the same time. Some
of them even take one-year full-time jobs __10__ they leave high school and then go to college.