In what year was the Cullinan diamond found?

The Cullinan diamond was discovered in 1905, making that the correct answer. This diamond is notable not just for its size—initially weighing an incredible 3,106 carats—but also for its significance in the history of gemology. The diamond was found in the Premier Mine in South Africa and was eventually gifted to King Edward VII of the United Kingdom. Its discovery marked a significant moment in the diamond's history, as it was the largest gem-quality diamond ever found at the time.

Other years listed in the choices do not correspond to the discovery of the Cullinan diamond. Specifically, 1901 predates the finding of the diamond, while 1910 and 1920 are also after its discovery. Therefore, those dates do not align with the historical account of the Cullinan diamond.