Bonjour
Est-ce que tu as pris les livres ce matin ?
les livres = masc. plur.
The pronoun for "les livres" = les
"les" is masc. & fem. plural
Oui, je les ai pris.
OR
Non, je ne les ai pas pris.
the past participle agree with "les= les livres" but doesn't change as "pris" has an "s" even in singular
If it was "Est-ce que tu as pris les affaires ce matin ?"
"les affaires" = fem. plur
"les" as I said is a masc.& fem. plural pronoun
Oui, je les ai prises
Non, je ne les ai pas prises.
it has to agree with "les" fem. plur. as it replaces "les affaires" ...
hope this will help ☺☺☺