Bonjour,
Réponse :
1)Richard was happy
→ Richard wasn't happy.
2)Ben bought a new bike
→ Ben didn't buy a new bike.
3)They wanted to go to London.
→ They didn't want to go to London.
Explications :
Au prétérit, pour tous les verbes ( sauf BE ) la forme négative:
sujet + didn't + base verbale
Verbe "BE"
I ; He; She; It wasn't
We ; You; They weren't