以已知线段AB为斜边的Rt△ABC的直角定点C的轨迹是( )。
以AB为直径的圆(A、B两点除外)
用所给词的适当形式填空。
1. My family _____ (decorate) our house before Christmas every year.
2. We _____ (celebrate) Christmas with a family meal.
3. I _____ (send) some Christmas E-card to my friends last year and I _____ (be) really happy to _____
(make) a contribution to the environment protection.
4. People always _____ (sing) Traditional Christmas songs at Christmas.
5. My mother with my little sister usually _____ (go) shopping before Christmas.
6. My classmate, Xiao Ming, never _____ (go) to the parks on weekends. She just _____ (do)
homework. She _____ (study) hard. But I _____ (not agree) with her. I _____ (think) she'd better
_____ (have) a rest after hard work.
7. Mike _____ (not feel) well. He _____ (feel) sick, and his parents _____ (look) worried.
几十年来计算机网络的发展经历了()阶段。
A.局域网
B.以单机为中心的通信系统
C.国际标准化的计算机网络
D.多个计算机互联的通信系统