During the period of the Roman republic there was direct democracy. Bills were voted by the popular assemblies: the Assembly of the Soldiers, the Assembly of the Tribes (voting districts) and the Plebeian Council. The Assembly of the Soldiers also elected the senior officers of state (the consuls, the praetors and the censors) and the Assembly of the Soldiers elected the junior ones (the aediles and the quaestors). So I would choose the letter to be Letter D (:
Hoped this helps.