The correct options are
A He preached that God is eternal.
B He promoted the idea of maintaining purity in character and behaviour to reach God.
C He spread the message of religious tolerance.
Guru Nanak focused on the idea of monotheism. He preached that God is one and is eternal. He promoted the idea of maintaining purity in character and behaviour to reach God. He spread the message of religious tolerance, universal brotherhood, and gender equality. He opposed rituals, idol worship, pilgrimages and social evils.