During the Roman Republic, civic duty was indeed an important part of life for citizens. Among the options given, the example of the moral obligations of all Roman citizens would be:
D. to vote in all elections for magistrates
This option reflects a key responsibility of Roman citizens to participate in the political process by voting, which was considered a vital part of their civic duties. While the other options may also represent important moral or civic aspects, voting was a direct responsibility tied to the governance of the Republic.