When did Hijra start?

a) 12th Rabi-ul-Awwal of 14th year of Nabawat
b) 12th of Rabi-ul-Awwal of 12th year of Nabawat
c) 12th of Rabi-ul-Awwal of 13th year of Nabawat
d) 12th Rabi-ul-Awwal of 10th year of Nabawat