Correct answer: C. Rigveda
Explanation: The direct answer is C, Rigveda. The four Vedas are Rigveda, Samaveda, Yajurveda and Atharvaveda. Rigveda is generally considered the oldest of them and contains many hymns addressed to deities. It is also an important source for understanding early Vedic society, beliefs and rituals. Option A, Samaveda, is mainly connected with melodies and chants used in performing hymns. Option B, Yajurveda, gives formulas and instructions connected with sacrifices. Option C, Rigveda, is the oldest Veda according to the standard school-history answer. Option D, Atharvaveda, contains material relating to everyday life, healing, spells and prayers and is regarded as later than the Rigveda. A helpful memory cue is: Rig means verses or hymns, Sama means song, Yajur means sacrificial formula, and Atharva is linked with everyday practices.