Bonjour
1- Mes livres ? Je les ai oubliés à la maison...
CORRECT the past participle agrees with the direct object "les" which is correct because it's before the verb.
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2- -Est-ce que tu te souviens de notre excursion en montagne ?
- Oui, je m'en souviens !
CORRECT the pronoun "en" is used to refer to "notre excursion en montagne."
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So everything is CORRECT !!!!!!!!!
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hope this helps ☺☺☺