光的世界十富多彩，光学器件在我们的生活中、学习中有着广泛应用．下列说法符合实际的是（　　）

如图，O是边长为a的正方形ABCD的中心，将一块半径足够长，圆心为直角的扇形纸板的圆心放在O点处，并将纸板的圆心绕O旋转，求正方形ABCD的边被纸板覆盖部分的面积为（   ）

Dear Anna，

    How are you these days? I'm1Shanghai and I live(居住)with Lin's family here.2people(人)are in3family—Mr. Lin，Mrs. Lin and Lin Feng.Lin Feng is Mr. and Mrs. Lin's4, and they are5to me.After school, I always play with Lin Feng.I can6him with his English and he can teach me Chinese.I7we can be good friends.I have a room here.It's nice and8.All of my books are in the bookcase and my computer is on the desk.In the evening, I read(读)books but I don't play games on9computer.Do you like Shanghai? You can10here next month.

Yours.

Bill