The correct answer is - D. People did not think the Earth was round.
The work of Newton on the gravitation received a lot of criticism mostly because his work was suggesting that the Earth was not flat, but that it was round instead. There were still only very few people that thought that the Earth is round in this period, and unfortunately they did not had proper proofs for it, thus the majority that still thought that the Earth is flat was ridiculing them, including Newton.
Since most of the people believed that the Earth is flat, they did not saw any reason why such force would even exist. Little did they new that Newton was actually on the right track and had discovered something that is so basic and so incredibly important for everything on the planet.
