Select the most appropriate option to substitute the underlined segment in the given sentence. If there is no need to substitute it, Select No improvement.Kumbh Mela, held at Prayagraj at the confluence of the rivers Ganga and Yamuna, is knowing to be the bigger human gathering in the world.

• A. is known to be the biggest human gathering
• B. No improvement
• C. has been known to be the bigger human gathering
• D. is knowing to be the biggest human gathering