Unless she had had an alarm clock, she would havemissed the train.（事实：她没有闹钟）
问题描述：
Unless she had had an alarm clock, she would havemissed the train.（事实：她没有闹钟）
中两个had是什么意思?
答
虚拟语气结构对过去的虚拟：had +动词过去分词
所以第一个had是助动词第二个是过去分词