A:40°
B:50°
C:80°
D:100°
一Did he play basketball after school yesterday?
— .He played soccer.
用显微镜观察“人体口腔上皮细胞”临时装片,观察到甲、乙视野.下列叙述正确的是( )
《九章算术》是东方数学思想之源,该书中记载:“今有勾八步,股一十五步,问勾中容圆径几何.”其意思为:“今有直角三角形,勾(短直角边)长为8步,股(长直角边)长为15步,问该直角三角形内切圆的直径是多少步.”该问题的答案是____步.