画[划]地为牢 （比喻只许在指定的范围之内活动draw a circle on the ground to serve as a prison ）
即：
restrict sb.'s activities to a designated area or sphere;
或 draw a circle on the ground as a house of detention （as a prison） for sb.
解析：
designated area
指定区域；指定地区
sphere [sfiə]
n.范围；球体
adj.球体的
vt.包围；放入球内；使…成球形
draw a circle
画一个圆圈
短语
show me how to draw a circle演示给我看怎么样画一个圆
