Which year was it that the library was built?

请问这里的 that the library was built 是什么从句？

它是定语从句吗？如果是，它修饰谁？句子是什么意思？

另外，可以看作是强调句吗？如何翻译？

【答】这是一个强调句（国外语法书叫“分裂句”： cleft sentecne），而且用了特殊疑问句式。

本句问的是“在哪一年图书馆被建造的？”，在which 前漏掉了In。如果随便问时间的话，就用When。

In which year was it that the library was built?

可能的回答：It was in 2016 that the library was built.

所以，介词in 不可省略。

When was it that the library was built?

可能的回答：It was in 2016 that the library was built.

可能的回答：It was last year that the library was built.

可能的回答：It was in October last year that the library was built.

关于强调结构的特殊疑问句式：

构成：疑问词+ is (was) it + that +句子的其他成分。特殊疑问词即是被强调的成分，例如：

Who was it that found your pen in the classroom yesterday?

When was it that the Second World War broke out?

Where was it that you lost your cell phone?

How was it that he managed to get my address?

How long ago was it that you last saw her?

What was it that had made you so sad?　　

Why was it that silver was not widely used as a conductor?　　

Which book is it that you want?　　

Whose umbrella was it that you took away?　

就划线部分提问举例：

It was in 2016 that the library was built.

→ In which year was it that the library was built?

It was in 2016 that the library was built.

→ When was it that the library was built?