A friend has decided to follow a vegan diet, giving up meat, fish, eggs, and dairy. What will be your friend's greatest dietary challenge?

A) Eating a variety of foods to ensure consumption of all the essential amino acids over the course of a day
B) Combining foods in such a way so as to obtain all the essential amino acids at every meal
C) Obtaining enough dietary fat
D) Obtaining enough calories to support necessary bodily functions