Bonjour,
Réponse :
5.He made the dress.
→ The dress was made by him
6. Somebody pushed Mary into the water.
→ Mary was pushed ( by somebody ) into the water.
7. People from all over the world visited the museum.
→ The museum was visited by people from all over the world.
Explications :
PASSIF:
be ( au temps de la voix active ) + participe passé
toutes les phrases sont au prétérit :
was + participe passé
Le complément d'agent introduit par "by" est souvent sous-entendu