这是我昨天找到的那把钥匙。

This is the key ___which I found yesterday.

这些是我们都知道的问题。

These are problems ___which we all know about.

你知道那家小意大利餐厅吗？就是我信里提到的那家。

You know that little Italian restaurant - the one ___which I mentioned in my letter?