Which answer matches this clue: the white marble monument in Rome housing the tomb of the Unknown Soldier?

• A Ara Pacis
• B Altare della Patria ✓
• C Castel Sant'Angelo
• D Arco di Costantino

The Altare della Patria, also called the Vittoriano, was built to honour Victor Emmanuel II and the unification; it opened in 1911.