The correct answer is: a) 1880.
The Manipur Rifles was a paramilitary force under British command that was formed in 1880. It was initially formed to protect the British Raj from the threat of the Burmese Empire. The Manipur Rifles played a significant role in the Anglo-Burmese War of 1885. After the war, the Manipur Rifles continued to serve as a paramilitary force in Manipur. It was disbanded in 1947, after India gained independence.
Option b) is incorrect because the Manipur Rifles was formed in 1880, not 1891.
Option c) is incorrect because the Manipur Rifles was formed in 1880, not 1907.
Option d) is incorrect because the Manipur Rifles was formed in 1880, not 1914.