Explanation:
The correct option is 'c'. For a trans-tibial amputation, the ideal bone length is generally between 12 and 15 cm (or roughly 5-6 inches) below the medial joint line. This length provides an adequate lever arm for prosthetic control and gait efficiency while preserving enough soft tissue clearance in the distal socket to accommodate the prosthetic foot and pylon mechanisms. Stumps that are too short lack control, and stumps that are too long cause fitting issues.

Reference: Pinzur MS, Gottschalk F, Smith D, et al. Functional outcome of below-knee amputation in peripheral vascular insufficiency. A multicenter review. Clin Orthop Relat Res. 1993;(286):247-249.