Explanation:
The correct option is 'd'. Böhler's angle is measured on a lateral radiograph of the calcaneus. The normal angle ranges from 20 to 40 degrees. In the setting of an intra-articular calcaneus fracture with depression of the posterior facet, Böhler's angle typically decreases and may even become negative. This indicates a collapse of the posterior facet and loss of calcaneal height.

Reference: Sanders R. Current concepts review: Operative treatment in 120 displaced intraarticular calcaneal fractures. Results using a prognostic computed tomography scan classification. Clin Orthop Relat Res. 1993;(290):87-95.