Concept:The first pledge of Aqabah was a historic agreement between Prophet Muhammad (peace be upon him) and a group of people from Yathrib (Madinah).Explanation:The pledge was made by twelve men from Yathrib who met the Prophet secretly at Aqabah.It took place in the 12th year of his prophethood, before the Hijrah (migration) to Madinah.This date corresponds to 621 C.E., which was after the Year of Sorrow and before the migration.The pledge laid the foundation for Islam to spread in Madinah.Answer:C. 621 C.E.