【正确答案】 C

【答案解析】[考点] 情态动词完成式表示虚拟 [解析] 题句是一个并列句，前半部分表示假设的结果，后半部分表示真实的情况，由连词but连接。这是一种隐含的虚拟语气结构，如：I would have gone to the hospital to see him, but I was too busy. “我本来是可以去医院看望他的，但就是太忙了(实际上没有去)”，暗含if I had not been so busy的假设条件。假设结果还经常用情态动词的完成式表达，如：They should have studied last night, but they went to the concert instead. “昨天晚上他们本该学习的，但去听音乐会了。”You needn't have dressed so formally, for it was only a family party. “你真不必穿得那么正式，不过就是一个家庭聚会嘛。”could have done表示“本来可以、本来能够(但实际上未并实现)”，如：I could have lent you the money, but you didn't ask me. “我完全可以借给你钱，但你没说呀。”所以根据题句的意思，C项是正确答案。