Complete the sentences with the correct relative pronoun or adverb :
1.We are talking about the boy /which, when, who/ won the competition.
2. We saw the house / whose, when, where/ agatha christie lived.
3.She doesn’t know / whose, who, what/ letter it was.
4.The ice-cream /what, which, whose/ I brought is in the fridge.
5.He knows the reason /why, that, which/ Helen is so upset.