D. The tribune could veto the magistrates' orders.
Explanation:
Initially, the tribunes protected individual plebeians from the arbitrariness of the magistrates. Gradually, a rather large power grown out of this right. Since 449, a person of tribune became inviolable, and his house had the right of asylum. The tribune could veto (ban) decisions of magistrates and the Senate (intercession law). Gradually, he became, as it were, the custodian of an agreement between the estates, and as such could take measures against uta violators (arrest, fine, etc.).
