In this exercise, here are the sentences in imperfect tense:

J'ai entendu une voix masculine que je ne connaissais pas. -- This is imperfect because the speaker is describing a state in the past. He didn't only not know the voice during the phone call.

Il avait mon numéro. -- The verb avoir (like the verb être and several other specific verbs) is almost always used in imperfect tense when talking about the past.

L'appel venait de votre fixe. -- This, in my opinion, could also be passé composé, depending on what the speaker wants to emphasize. In this case, the speaker views the call as a kind of background action during which everything else happened. It is an event of some duration which concluded in the past.

Hi Thanh Tân,

This is an aspect of French grammar that causes some confusion so you are not alone in this regard.

There have been many posts dealing with this issue.

Briefly, if in English it were possible to substitute "was" "were" or "would" -- ("would" meaning an habitual past action) then you should be able to expect to use l'imparfait.

However if the action was completed in the past you would normally expect to use the Passé Composé.

This is meant to be an overview, not an exhaustive explanation.

Hope it helps.

Jim

Hi Thank Tân,

Another link has just been posted by Laura Lawless:-

https://www.lawlessfrench.com/grammar/passe-compose-vs-imparfait-3/?utm_source=mailpoet&utm_medium=email&utm_campaign=lawless-french-language-myths-passe-compose-vs-imparfait-meaning-bidonner-mot-du-jour-3593

This will give you a good reliable reference going forward.

Bonne continuation

Jim