'Imphal Basin' surrounded by Manipur hills is fine example of

1. A

   Lacustrine plain

   (a) Lacustrine plain. The Imphal Basin is a former lake bed around Loktak; sediments of that lake built a flat intramontane floor ringed by Manipur hills. That origin is the official key.

2. B

   Loess plain

   (b) Loess plain. Loess is wind-laid silt (Malwa, parts of China). Imphal is not an aeolian fill.

3. C

   Glacial plain

   (c) Glacial plain. Pleistocene ice did not plane this valley into a till plain; the basin is lacustrine, not glacial.

4. D

   Alluvial plain

   (d) Alluvial plain. Rivers rework the floor, but the textbook genetic label for Imphal is lacustrine (lake-laid), not a Himalayan alluvial doab.

Summary. Official key is (a) lacustrine plain. Imphal Basin, closed by Manipur hills and holding Loktak Lake, is a classic lake-plain. Loess, glacial and generic alluvial labels are the wrong genesis. Honour the stored letter (a).