поставив сказуемое в страдательный залог

1. The Romans completed the Colosseum in 82 AD.

2. I lost the key yesterday.

3. We will translate the text tomorrow.

4. I will ask many questions when he stops speaking.

5. The teacher explained all the meanings of the world.

6. Millions of tourists vizit London every year.

1) The Colosseum was completed by the Romans in 82 AD.

2) The key was lost yesterday (можно ещё добавить в конце by me, хотя вовсе необязательно)

3) The text will be translated tomorrow (опять же, можно добавить в конце by us, а можно и не добавлять).

4) When he stops speaking, many questions will be asked (по желанию в конце by me)

5) All the meaning of the world were explained by the teacher.

6) London is visited by millions of tourists every year.