Réponse :
Bonjour,
Tu dois rétablir la vérité en disant ce que les personnes faisaient.
Il faut utiliser du prétérit "be" + ing = was / were + V-ing
Pour dire ce qu'ils n'étaient pas en train de faire ( ce qui est barré dans chaque phrase de ton exercice ) , il faut utiliser la fomr négative.
wasn't / weren't + V-ing
a. At 10 o’clock Jeff and Laura weren’t kissing behind the library, they were talking.
b. Last night, Jake wasn’t having a party, he was sleeping in his room.
c. Lucy wasn’t laughing and chatting during the math test, she was working hard.