Bonjour,
Réponse :
a. The giant was having dinner in the forest, when he saw a strange creature.
b. While Conor was reading a book in his bedroom, he realised that he had
not done his homework yet.
Explications :
Prétérit Be + V-ing: s'utilise pour décrire les actions qui étaient en cours
Prétérit simple: pour les actions qui viennent interrompre les actions en cours