The correct answer is C. In Keshav’s house, ‘puja’ was performed.
During the Puja days’, people visit those houses where ‘puja’ is performed. They make it a point to go even if they are not invited. Manmohan visited the house of Keshav, his office colleague, during ‘puja days’. This implies that Manmohan visited Keshav’s house because Keshav was performing puja. It is unlikely that Manmohan, being a religious man, went to Keshav’s house uninvited, as this would be considered rude. It is also unlikely that Keshav had invited Manmohan for some other function, as Manmohan would not have gone to Keshav’s house if he had not known that puja was being performed.