The State of Aurora requires licenses of persons "who are engaged in the trade of barbering." It will grant such licenses only to those who are graduates of barber schools located in Aurora, who have resided in the state for two years, and who are citizens of the United States. Which of the following is the strongest ground on which to challenge the requirement that candidates for barber licenses must have been residents of the state for at least two years?
The privileges and immunities clause of the Fourteenth Amendment The due process clause of the Fourteenth Amendment The equal protection clause of the Fourteenth Amendment The obligation of contracts claus