The correct answer is:
b. Were frequently assassinated.
Explanation:
Political instability followed Mexico after the independence, leading to the Mexican Revolution, were citizens protested against the reign of Porfirio Diaz, once Porfirio Diaz was overthrown, Mexico continued experiencing political instability because the political leaders were frequently assassinated.
Emiliano Zapata and Pancho Villa were the leaders of the Revolution, but were killed during the war. Afterwards, Francisco Madero became president and was assassinated by Victoriano Huerta who then came into power as a dictator, he was then replaced by Venustiano Carranza who finally brought political stability to Mexico, and created the Mexican Constitution of 1917. Even after Carranza's presidency came to an end, he was also assassinated.