Correct answer: D. They could veto any law or action of a magistrate.
Context/detail:
In the Roman Republic, farmers, merchants and artisans eventually gained the power to elect tribunes who represented them in government and could veto the actions of consuls and other leaders, protecting the interests of the common people (the "plebeians") whom they represented.
"Tribunis Plebis" was the Latin term for "Tribune of the people" (the plebs). "Concilium Plebis" was the Latin name for the Plebeian Council or assembly. There had been assemblies of the plebeians before plebeian unrest that reached a crisis stage in 494 BC. But after that date, plebeian assembly's actions, under the authority of the tribune of the people, carried more official authority. The creation of the office of tribune, to represent the people and offset the power of the consul, occurred after major conflict between the plebeians and the ruling class (the patricians) in 495-494 BC.