. Father said we were lucky not to leave our visas at home. Otherwise, we ______to go back home.A. would have hadB. wouldn't haveC. would haveD. wouldn't have had

步骤 1：理解句子结构
句子的主句是 "Father said we were lucky not to leave our visas at home."，其中 "Father said" 是主句，"we were lucky not to leave our visas at home" 是宾语从句。从句中的 "not to leave our visas at home" 是一个否定的不定式短语，表示我们没有把签证留在家里，这是幸运的。
步骤 2：分析虚拟语气
"Otherwise" 引导的从句表示与事实相反的假设，即如果把签证留在家里，那么我们就会不得不回家。这里需要使用虚拟语气，表示与过去事实相反的情况。
步骤 3：选择正确的虚拟语气形式
与过去事实相反的虚拟语气，主句的谓语动词形式为 "would have done"。根据句子的语境，这里需要表达的是 "不得不回家"，所以选择 "would have had to"。