Final answer:
In French passé composé, 'ont marché' is the correct conjugation to use for 'Elles marcher toute la journée'.
Explanation:
The correct conjugation of the verb in passé composé for 'Elles marcher toute la journée' is 'ont marché'.
The passé composé tense in French is used to indicate completed actions in the past.
In this sentence, 'ont marché' is the correct conjugation where 'ont' is the auxiliary verb avoir and 'marché' is the past participle of 'marcher'.
Learn more about French verbs in passé composé
