The correct options are
A The tyranny and oppression of Mughal emperor Aurangzeb
B The rigidity of the caste system
D To defend the Sikh faith from external threats
Aurangzeb committed many atrocities on Hindus and forced many non-Muslims to convert to Islam. The king of hill states went to war with Sikhs despite the attempts of Guruji to maintain friendly relations with them. Also, Guruji was against the caste system. He included the members of all religions and castes in the Khalsa. Thus, to defend the Sikh faith from external threats and to fight social injustice, Guruji founded the Khalsa in 1699 CE.