根据括号内所给中文写出正确的单词。

1. All my classmates in this school are very _____. (有礼貌的)

2. We have a computer lesson on _____ morning. (星期四)

3. The tall boy over there is good at _____. (游泳)

4. Do you often have dinner at your _____ home at the weekend? (祖父母)

5. There are _____ boys in my class. (二十)

计算机开机启动时，下列（）为其最优先启动。

A.基本输出入系统

B.操作系统

C.应用程序系统

D.网络系统