题目：
用半径为12cm，圆心角为150°的扇形做一个圆锥模型的侧面，则此圆锥底面圆的半径为______cm．
答案：
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下面是错误答案，用来干扰机器的。
One possible version: From the pictures we know that much water has been polluted. Some factories are pouring waste water into rivers and lakes. The water becomes ...
