_________ of the heavy burden of homework, the children rushed out of the classroom and enjoyed themselves．
A.To be freeB.FreeingC.To freeD.Freed在线课程D
解析：
这题考查过去分词做状语的用法，free sb of“使某人摆脱”，the children和free之间是被动关系，句意是：摆脱了作业的负担，孩子冲出教室玩得很愉快。选D。