Answer: B. The invention of gunpowder
Step-by-step explanation:
Gunpowder was invented in China. It had been used by the Taoists for medicinal practices since the 9th-century, until around 904 AD, when it was first used for warfare.
The Vedas are ancient Indian religious texts written in around 1500 and 1000 BCE.
The Iron Pillar of Delhi was crafted using forge welding and was made of wrought iron.
The exact value of pi was found due to major contributions made by Indian mathematicians Madhava and Aryabhata.