They aren’t.
At least I don’t think so…
Imparfait would be the description of a situation for example :weather, landscape, person in the past whilst passé composé are actions that suddenly happened for example, interrupting another action. Passé composé you would also use an auxiliary like either avoir or être then you would add the verb
Answer:
Paul et Lucie sont de Belgique.
Ummm... here I only translated for others
correction of the text "thing of the evening" by victor hugo 6eme
A) Nous l'avons entendue
Here the past participle match the the direct object( femenine singular)because it goes before the verb.
Nous avons entendu la chanson/Nous l'avons entendue