Option a is the correct answer. Chandragupta-I was the founder of the Gupta dynasty and the first ruler to establish the Gupta Samvat (also known as Vallabhi Era), a calendar system that was used in ancient India. The Gupta Samvat started from 320 CE , which is considered as the year of Chandragupta-I's coronation. The Gupta Samvat was also known as the Malava era or the Vikramaditya era, as Chandragupta-I adopted the title of Vikramaditya, meaning "the sun of valour". The Gupta Samvat was widely used by the Gupta rulers and their successors for dating their inscriptions, coins, and documents. It was also used by other regions and countries that were influenced by the Gupta culture, such as Nepal, Bengal, Kashmir, and Southeast Asia. The Gupta Samvat was one of the most important calendar systems in ancient India and reflected the political and cultural supremacy of the Gupta Empire. Important Tips Various Calendar Eras of Ancient India: Buddhist Era: This era based on Buddha's birth and date. The dates of Buddha's birth and date are uncertain but as per current theravada and Sri Lankan traditions, the Buddha Era begins from 544 BCE. Jain Era {Vira Nirvana Samvat}: Vira Nirvana Samvat began on 15 October, 527 BCE and commemorates the nirvana of Mahavira. The Saka era: This is the oldest and most widely used calendar system in India. It started from 78 CE , which is considered as the year of the coronation of Kanishka, the Kushan king who ruled over northern India and Central Asia. The Vikramaditya era: It started from 58 BCE, which is considered as the year of the coronation of Vikramaditya, a legendary king of Ujjain.