题目

One of the most important things in the world is friendship. In order to have friends, you have to be a friend. But how can you be a good friend at school? Listen--Listen when they are talking. Don’t say anything unless they ask you a question. Sometimes it’s not necessary for you to have anything to say; they just need someone to talk to about their feelings. Help them--If your friend is ever in need of something, be there to help them. You should try to put them first, but make sure you don’t do everything they want you to do. Try to take an extra(额外的)pencil or pen with y 下图是一个隧道的横截面，若它的形状是以点O为圆心的圆的一部分，路面AB＝10米，高CD＝7米，则此圆的半径OA等于 [　　] A． 5 B． 7 C． D．