The correct answer is: A. Agni
Agni is the Vedic god of fire, the eldest son of Dyaus Pita (Sky Father) and Prithvi (Earth Mother). He is the messenger between the gods and humans, and is invoked in every Vedic ritual. Agni is also the god of war, and is often depicted as a warrior with a flaming sword.
Indra is the Vedic god of thunder and lightning, and the king of the gods. He is the most important god in the Rigveda, and is often invoked in battle. Indra is also the god of strength and virility, and is often depicted as a warrior with a thunderbolt.
Surya is the Vedic god of the sun, and is the personification of light and life. He is often depicted as a charioteer driving a chariot across the sky. Surya is also the god of law and order, and is often invoked in times of trouble.
Varuna is the Vedic god of the sky and the ocean, and is the god of law and order. He is often depicted as a wise old man with a long beard. Varuna is also the god of fate, and is often invoked in times of uncertainty.
In conclusion, Agni is the Vedic god of fire, and is regarded as the War-God in Rigveda.