The correct answer is: c) Bishnupur.
Bishnupur district has the largest navigable river system in Manipur, enabling water transport. The Imphal River, which flows through the district, is the largest river in Manipur. The Imphal River is a major source of irrigation for the district and is also used for transportation. The Imphal River is navigable for about 100 kilometers from its source in the hills to its confluence with the Barak River in Assam.
The other options are incorrect because they do not have a large navigable river system. Imphal East district is located in the central part of Manipur and does not have a large river system. Ukhrul district is located in the north-eastern part of Manipur and does not have a large river system. Churachandpur district is located in the south-western part of Manipur and does not have a large river system.