句意：他本应该完成学业,但现在不得不退学找工作赚钱养家。这句话过去时间段的虚拟语气，主 句谓语动词采用would/should/could/have+过去分词，从句谓语had+过去分词，而从句是可以省略的。这句 话补充完整应是：If he had money, he would have finished his college education, but he had to quit and find a job to support family.此处but转折后跟的是had to do用法，从句采用过去时，与虚拟语气无关。因此，本题的正 确答案为C。