The correct answer is (a) 1785 A.D.
The Gorkhas were a group of people from Nepal who invaded Kumaun (Almora) in 1785 A.D. They were led by Prithvi Narayan Shah, who was the founder of the modern state of Nepal. The Gorkhas were able to conquer Kumaun because they had a much larger army than the local rulers. They also had better weapons and equipment. The Gorkhas ruled Kumaun for many years, and they had a significant impact on the culture and society of the region.
Option (b), 1790 A.D., is incorrect because the Gorkhas actually conquered Kumaun in 1785 A.D.
Option (c), 1775 A.D., is incorrect because the Gorkhas did not invade Kumaun until 1785 A.D.
Option (d), 1780 A.D., is incorrect because the Gorkhas did not invade Kumaun until 1785 A.D.