Passé composé: Meaning changes with Être and Avoir

Generally, the verbs descendre, monter, passer, rentrer, retourner, and sortir use être. They may, however, take avoir as their helping verb when they are used with a direct object. The meaning of these verbs differs according to the auxiliary verb that is used:

Descendre: with être, got off, went down; with avoir, took down
Monter: with être, went down; with avoir, took up, set up
Passer: with être, passed by, dropped; with avoir, spent
Rentrer: with être, came in; with avoir, brought in
Retourner: with être, returned; with avoir, turned over
Sortir: with être, went out; with avoir, took out

Demander = to ask Se demander = to wonder