a)   They would perform a Rajasuya sacrifice to release Indra from any sin thus incurred
b)   They would perform a Asvamedha sacrifice to release Indra from any sin thus incurred
c)   No sin would Indra thus incur because Vrtrasura was from the family of demons
d)   Indra could later perform meditation

The correct answer is
b)   They would perform a Asvamedha sacrifice to release Indra from any sin thus incurred