Her dedication to studying really paid off when she aced the exam.

paid 是动词 pay 的过去式，pay 本意是"支付、付款"。 off 在这里是副词，表示"完全地、彻底地"。 paid off 是固定短语，意思是"得到回报、取得成功"，指付出努力后获得好的结果。