Passé Composé & Passive Agreement
When a verb uses être to form the passé composé, the past participle agrees with the subject.
Les femmes sont descendues.
The women descended.
Aujourd'hui maman est morte. Ou peut-être hier.
- L'Étranger d'Albert Camus
Today mother died or maybe yesterday. The StrangerLa liberté est née en Angleterre des querelles de tyrans.
- Voltaire
Liberty was born in England from the quarrels of tyrants.
When the passé composé is formed with avoir, the past
participle never agrees with the subject. It can only agree with the preceding
direct object when the conditions described on the previous page are met. 
PassivesLa femme a retourné l'argent.
The woman returned the money.
In passive sentences, the past participle always agrees with the subject.
Ces enfants sont aimés par tout le monde.
These children are loved by everyone.Marie a été enlevée par le monstre.
Marie was taken away by the monster.