A student set up the experiment shown below to determine if radish seeds take in oxygen as they germinate. Methylene blue is a chemical that is blue when oxygen is present, but is colorless when oxygen is not present. Containers A and B each contained 200 mL of water and 10 drops of methylene blue. Ten radish seeds were added to container A. Container B had no radish seeds. The purpose of container B in this experiment is to

A. show that seeds do not give off oxygen

B. serve as the experimental container

C. show that seeds do not give off carbon dioxide

D. serve as the control container