Which option distinguishes why Djimon is gaining weight in the following scenario?

Djimon moved to the United States from France, where portion sizes are much smaller. He found that after six months, he had gained thirteen pounds even though he only ate what he was served.

A. He did not eat fast food in France.
B. He does not understand serving sizes.
C. American meals contain more calories.
D. French meals include more vegetables.