Answer:
Usually families take the dinner in the dining room, which in spanish is called El comedor. This is the place where the members of a family or a group of people gather to eat food (the breakfast, the lunch, the dinner or a snack) and talk.
The other places of the house, such as, the bedroom (el dormitorio), the bathroom (el baño), the kitchen (la cocina) and the living room (sala de estar), are not the usual places to take the meals.
Therefore, the right answer is:
El comedor