Option d is the correct answer. Onam is a festival that commemorates King Mahabali, who was a benevolent and generous ruler of Kerala. According to a popular legend, Mahabali was so loved by his subjects that the gods became jealous and sent Vishnu in the form of a dwarf named Vamana to test him. Vamana asked Mahabali for as much land as he could cover in three steps, and Mahabali agreed. Vamana then expanded his size and covered the earth and the sky in two steps, leaving no space for the third step. Mahabali offered his head as the third step, and Vamana pushed him down to the underworld. However, Vishnu was pleased with Mahabali's devotion and granted him a boon to visit his people once a year. Onam is celebrated to welcome Mahabali's spirit to Kerala.