什么情况下用什么时态的疑问句提问？

Hi All,以下有两个句子：

1.What did you see? 2.What had you seen?

我想问一下，什么情况下才会用到句型1来提问，句型2呢？

可否详细解释一下并且举几个实例好吗？有点儿不理解，先谢谢各位了～！
请看看这里有篇课文：
Nearly a week passed before the girl was able to explain what had happened to her.One afternoon she set out from the coast in a small boat and was caught in a storm.Towards evening,the boat struck a rock and the girl jumped into the sea.Then she swam to the shore after spending the whole night in the water.During that time she covered a distance of eight miles.Early next morning,she saw a light ahead.She knew she was near the shore because the light was high up on the cliffs.On arriving at the shore,the girl struggled up the cliff towards the light she had seen.That was all she remembered.When whe woke up a day later,she found herself in hospital.

Comprehension:
1.What had she seen high up on the cliffs?(这里为什么用完成时态来提问呢？用句型1来提问可否？)
如果换成What did she see high up on the cliffs?来提问会使人产生误会吗？我觉得很有必要弄清楚

1 对过去发生的动作提问，用到的是一般过去时

2 这个问句的时态是过去完成时，通常不单独使用。

例句：
1 I worked in that factory six years ago.

2 I have worked in that factory since last year.

3 I had worked in that factory for six years before 2005.

仅仅表示过去发生过的动作，就用一般过去时（例1）
表示过去发生的动作和现在有关或者延续到现在，用现在完成时（例2）
如果表示在过去的某个时间以前发生的动作，用过去完成时 （例3）

现在完成时属于现在时间范畴
一般过去时和过去完成时属于过去时间范畴

如果在句子中没有明确的表示过去时间的时间状语，通常只用一般过去时而不用过去完成时。
所以（例3）中如果没有before 2005，那么就可以写成：
I worked in that factory for six years.（我曾在那个工厂工作了六年。）
与I worked in that factory six years ago.(六年前我曾在那个工厂工作。）
是不同的两句话。

补充：
1 这里提问What had she seen high up on the cliffs?用到had seen是因为文中这两个句子She knew she was near the shore because the light was high up on the cliffs.On arriving at the shore,the girl struggled up the cliff towards the light she had seen.

这里用到了had seen是因为上文已经提到she看到了the light，see这个动作是在struggle这个动作之前发生的，所以用had seen，表示在过去的过去发生的动作。