The correct option is D Despite being exposed to nature's elements for centuries, it has not yet corroded.
Iron-made objects had been common since the ancient civilisations in India. Vijaya Stambha, a 24 feet high pillar weighing 7 tonnes was built by Chandragupta II. However, what makes it special is that despite being exposed to nature’s fury over many centuries, it has not yet corroded. It is one of the examples to prove the advancements in science in ancient India.