Approfondir belong to the 2
nd group. Approfondir is a common french verb.
Approfondir is conjugated the same way that verbs that end in :
-ir
Approfondir is conjugated with
auxiliary avoir.
Approfondir verb is
direct transitive.
French verb approfondir can be conjugated in the reflexive form:
S'approfondir
Approfondir verb is a direct transitive verb, so passive voice can be used.