对比、分析、归纳是学习化学的重要方法．
一个圆锥的底面圆的周长是2π，母线长是3，则它的侧面展开图的圆心角等于（ ）
—He wanted a job, _______could help him support his family.
( 1 )估计结果____厘米
( 2 )测量结果____厘米
