| Who / that refer to people
|| They caught the man Who / that spied for china.
| Which / that refer to objects
|| I lost the map which / that she gave me.
| Whose refers to possession
|| She complained to the man whose dog bit her.
| When refers to a moment in time
|| Christmas Day is a day when people are happy.
| Where refers to a particular place
|| We visited the house where our father was born.
| In non-defining sentences, the word that cannot replace who or which.
|| Mata Hari, who was a famous female spy, was born in holland. Buckingham Palace, which is in London,is a favourite tourist site.