Sometimes I feel that being the mother of three small children is like operating a large circus(马戏团)． 21 afternoon last week, my three sons playing peacefully in the back yard ( 院子), 22 the ball from one to another．I jumped at the chance to talk to one of my friends 23 the phone, but before I 24 to the phone, I could tell the boys had begun to quarrel with each other about something．I rushed out to 25 peace,but before I got there Charles had 26 a rock at Mark,and hit him in the eye．By the time I got to the back yard,they had begun to 27 about this．Even David,the oldest boy,who won' t usually fight with anybody about 28 ,was involved(卷入) First,! 29 them stop fighting, and then ! examined Mark' s eye．I decided that it wasn' t going to develop into a black eye, but I felt that they should 30 at least a little for 31 they had done． I' m going to 32 to your father about this when he comes home tonight, I said． He and I will think of how to punish you． Things were 33 quiet after that for about half an hour, and then Charles 34 a glass in the kitchen,and at almost the same 35 ,Mark fell out of the apple tree． 第（31）题答案
A.fight
B.that
C.things
D.what
和过y轴的平面的交线是圆，则圆的半径为（ ）。
