Portion sizes in American restaurants have been increasing steadily, so much so that people from other cultures are surprised by how much food they get at American restaurants. Why are restaurants unlikely to change their portion sizes even though they know that it would be healthier to provide smaller portions?

A. Large portions are the norm and diners now expect them.

B. Portions grew because diners complained that they did not get enough food.

C. Once a behavior is established in a culture, it is almost impossible to change.

D. There is no incentive for restaurants to change the culture and reduce portion sizes.