Choose the right forn of the verb and write down the sentences

1.We already(were,have,been)to London
2.We(were,have,been) in London 5 years ago.
3.They(didn't see,haven't seen)the Tsar Bell when they were in Moscow.
4.They(didn't see,haven't seen) the Tsar Bell yet.
Помогите пожалуйста.