Option c is the correct answer. The Hunas were a nomadic people from Central Asia who invaded India in the 5th century CE. The Hunas were skilled warriors and they were able to defeat the Gupta Empire, which was the dominant power in India at the time. The Huna invasion caused widespread destruction and disruption, and it led to the decline of trade and commerce in India. The Indian merchants were forced to look for new markets, and they turned to Southeast Asia. The maritime trade with the regions of South-East Asia, such as Indonesia, Malaysia, Thailand, Cambodia, Vietnam, etc., flourished during this period. The Indian merchants also spread their culture, religion, and language to these regions.