Final answer:
The formal constitutional requirement for becoming president is being a natural-born citizen of the United States, being at least 35 years old, and residing in the United States for at least 14 years.
Step-by-step explanation:
The formal constitutional requirement for becoming president is that the individual must be a natural-born citizen of the United States. This means that a person must be born as a citizen of the U.S. and not have acquired citizenship through naturalization.
In addition to being a natural-born citizen, the person must also be at least 35 years old and have resided in the United States for at least 14 years.
Other requirements include that the individual must be at least thirty-five years old and must have been a permanent resident in the United States for at least fourteen years. Therefore, the correct answer to the student's question is C. must be a natural-born citizen.