过去完成时是英语中表示过去某一时间或动作之前已经完成的一种时态。那么，当我们需要将一个过去完成时句子变成疑问句时，应该如何进行呢？
以下是过去完成时变疑问句的方法：
- 将助动词"had"提前到主语前面，使其成为句子的开头。
例如：He had finished his homework before he went to bed. → Had he finished his homework before he went to bed?
- 使用疑问词来引导疑问句，通常疑问词为"who, what, when, where, why, how"等。
例如：She had already eaten breakfast when we arrived. → What had she already done when we arrived?
- 当疑问词是"how"时，需要在后面加上一个形容词或副词。
例如：I had never seen such a beautiful sunset before. → How had you never seen such a beautiful sunset before?
以上就是过去完成时变疑问句的方法。学好过去完成时的语法，对于我们的英语学习和使用都有很大的帮助。希望这篇文章能够对大家有所帮助！
