我国在大力发展空间技术方面，成功发射的第一颗人造地球卫星是（　　）

     My friend Tony is an American1 . He is ten years old. He lives 2  his family in China now. There are 3  people in his family; his mother Mrs Green, his father Mr. Green and his little sister Amy. He has a white cat. 4  name is Betty. Look ! Amy is playing 5  Betty. His father, Mr. Green,is watc­hing TV. His mother is doing housework. What about Tony? He is doing6 Chinese homework. He can't 7   Chinese well, but he likes Chinese very much.
    Tony's 8 works in a TV station. His father works in a school as an9 teacher. Tony and his sister10 to the same school.

如图所示，点D在⊙O的直径AB的延长线上，点C在⊙O上，且AC=CD，∠ACD=120°．

（1）求证：CD是⊙O的切线；
（2）若⊙O的半径为2，求圆中阴影部分的面积.