The correct answer is: a) Imphal Valley.
Cord-marked pottery is a type of pottery that is decorated with cord impressions. It is a distinctive prehistoric artifact type that has been excavated in many parts of the world, including Manipur. In Manipur, cord-marked pottery has been found in the Imphal Valley, which is the most densely populated region of the state. The pottery is thought to have been made by the Meitei people, who are the indigenous people of Manipur. Cord-marked pottery is dated to the prehistoric period, and it is thought to have been used for a variety of purposes, including cooking, storage, and ritual.
The other options are incorrect because they are not regions of Manipur where cord-marked pottery has been excavated. Bishnupur District is a district in the southern part of Manipur. Chandel District is a district in the western part of Manipur. Churachandpur District is a district in the northeastern part of Manipur.