The pop up translation of century says "la centana" but marked it wrong
The translation says "centena"
You can use centuria instead. La centuria empieza hoy.
Hoy el siglo empieza
Why wrong? I keep getting these answers wrong... I guess Hoy no es mi dia (can't put the accent...)
usually the subject follows the verb -- only a guess
Word order isn't critical here, so I'd report your answer as correct