Correct Answer:
A. A. 30 years
The reign of the Rightly Guided Caliphs (Rashidun Caliphate) lasted for approximately 30 years, from 632 AD to 661 AD. This period followed the death of Prophet Muhammad and included the rule of Abu Bakr, Umar, Uthman, and Ali. Options B, C, and D are incorrect as they do not represent this historical duration.