根据短文理解选择答案。
The students start arriving on our playground from about 8:45 am. Most of our children walk but some travel to school by car.
The children wear a school uniform and carry their homework and lunch in a school bag.
School begins at 8:55 a.m. The duty teacher blows a whistle and the children line up in their class groups. They wait quietly for the teacher to send them to their classrooms.
On arriving in their classrooms, the children empty their bags and put their homework in the marking boxes. The children then go back into their classrooms.
The children do their early morning work while their class teacher takes the attendance register(考勤簿).The teacher reads out each child’s name in turn. At 9:10 a.m., the children go to assembly in our main hall. They sit on the floor in rows with the youngest children at the front and the older children at the back. As the children go into the hall, they listen quietly to the music playing.
是正方形，对角线
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在以 
为圆心的圆上.
