Mrs. DR Vandertramp helps us remember B. which verbs use être instead of avoir for the passé composé.
Mrs. DR Vandertramp is actually an acronym - an acronym is a word made up of first letters of several words. So, in this case, Mrs. DR Vandertramp stands for: monter, retourner, sortir, venir, arriver, naître, descendre, entrer, rester, tomber, rentrer, aller, mourir, and partir, all of which are verbs which use etre instead of avoir to form passe compose tense in French.