Final answer:
Corn is considered a staple in the Mexican diet, originating from an ancient grass and selectively bred to become a primary source of food in Mexico.
Step-by-step explanation:
Among the options provided, corn would be considered a staple in the Mexican diet. Corn, also known as maize, has been a fundamental food item in Mexico since its development from a native grass called teosinte around 9,000 years ago.
This crop was selectively bred by ancient Mexican farmers, primarily women, to produce more and bigger seeds. Corn has become not only a crucial staple crop in Mexico but also the most-grown grain crop globally, significant for both human and animal consumption as well as in various industrial applications.
In comparison, peas are less central to the Mexican diet, while rice and olive oil are more commonly associated with other cuisines. Rice does play a role in the Mexican diet but not to the extent of corn. Olive oil, while used in cooking, is not considered a staple food item integral to the traditional Mexican diet.