呼吸是动物重要的生理特征，不同的动物的呼吸结构或器官差异很大，但功能都是最大限度的吸收氧气，排出二氧化碳．请结合下面的图解和有关实验分析回答问题：

A

    I have five children. I'm always busy when they're awake(醒着)．That's why I try to get up before everyone else. I get up at 5：00 a．m．The house is quiet．I drink a cup of coffee and read books．I love that time because it's mine and I can think without interruptions(打扰)．

    ——Anna

    I'm a night person．I love the night．I feel sleepy all day and then at night l wake up! I like to dance．watch movies or talk to friends at night．I never go to sleep before 2：00 a．m．

——James

    I'm a morning person．As soon as a little light(光)comes through the window(窗户)，I wake up and start my day．I try to do important work in the morning because I know that I think best at that time．After 1：00 p．m．. I begin to slow down!

    一Sandra

    I love tea time．I like to have tea in late afternoon．It's a time to stop the day's activities for an hour and talk with Mends．Sometimes, people visit my home then．Sometimes，I go to a friend' s house for tea．

    —Bob

如图所示的向日葵图案是用等分圆周画出的，则⊙O与半圆P的半径的比为（　　　）