圆周上各点离圆心的距离相等。All points on a circle are equidistant from the centre.圆周内两直径必相交.Any two diameters of a circle intersect each other.圆的直径与圆周有相互关系.The diameter and the circumference of a circle correlate....
MEI Shi - long , 1991 . Middle and Late Cambrian conodont and trilobite biostratigraphy in Wanxian, Hebei . Unpublished Ph. D thesis of Peking University.武桂春, 2003. 鲁西地区晚寒武世牙形石. 北京大学博士研究生学位论文....an unpublished PhD thesis...