Many of you would know that der/das/die are definite, while ein/eine are indefinite articles. In the below sentence, you will be often tempted to enter `ein`, but it is actually wrong.

Das ist _______ Auto von Bernard.

The answer is `das`. why? if you observe closely the gender for Auto is `das` and ein is indefinite article. Since the auto (car) clearly belongs to Bernard, it becomes definite.

Das ist das Auto von Bernard

Keep in mind that the moment you see `von` and the Persons Name the answer will be definite article.