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https://progress.lawlessfrench.com/revision/glossary/transitivity

https://progress.lawlessfrench.com/revision/glossary/transitivity/transitive-verb

Retourner can be used with avoir or être in compound tenses depending on its meaning in French (Le Passé Composé)

Grammar Jargon:   
partir and sortir are intransitive verbs, whereas quitter and laisser are always transitive verbs (i.e. have a direct object).

In this lesson the comment is made that «quitter and laisser are always transitive verbs - ie have direct objects» . While both parts of the statement are correct, it seems to link the need for a direct object to be the definition of being a transitive verb. It is the definition only for «les verbes transitifs directs». (In other lessons as for 'retourner' here the same inference is given by noting that retourner is «intransitive because it lacks a direct object»). 

In a number of other references, and discussed fully on the KwizIQ glossary pages linked, the definition for 'transitive verb' is that it needs an object, with some verbs only taking direct objects, some indirect objects, and some taking both. Some verbs are intransitive - cannot have any object. There are of course verbs that have both transitive and intransitive usage. So as not to repeat everything, I will just note that the 'description' of these forms in lessons is not always consistent with their 'definitions'.