Explanation:
The correct option is 'a'. A Holstein-Lewis fracture is a spiral fracture of the distal one-third of the humerus. In this injury, the radial nerve is particularly at risk of being tethered or lacerated by the lateral intermuscular septum or the fracture fragments as it passes from the posterior compartment to the anterior compartment of the arm.

Reference: Holstein A, Lewis GB. Fractures of the humerus with radial-nerve paralysis. J Bone Joint Surg Am. 1963;45:1382-1388.