The correct option is C Rigveda
The Vedas are the earliest surviving literature of Indian subcontinent. There are four Vedas: the Rig Veda, the Sama Veda, the Yajur Veda and the Atharva Veda. Of these the Rig Veda is the oldest and was composed about 3500 years ago. All the other Vedas are based upon it and consist to a large degree of various hymns from it. It consists of a thousand such hymns of different seers, each hymn averaging around ten verses. The Rig Veda is also the oldest book in Sanskrit or any Indo-European language.