Martin is buying a fish tank. For the tank, he wants 10 clownfish, a few plants, and some stones for the bottom. He wants to make sure that the tank is large enough for the fish to swim comfortably. What does he need to ask the salesman in order to make sure he buys a large enough tank?

A What type of food do clownfish eat?
B How long do clownfish typically live?
C What kind of plants do clownfish like?
D How much space do clownfish need to swim?