Fill in the gaps using the Passive Voice:1)Millions of books____ in

Fill in the gaps using the Passive Voice:
1)Millions of books____ in Russia last year. (publish)
2)A lit of animals ___ every year (kill)
3)The treasure ____ in three years (find)
4)The keys ____ already (find)
5)The problem ___ before he phoned (discuss)
6)The cake ____ at the moment (make)