Explanation:
The correct option is 'a'. The scaphoid receives the majority of its blood supply from branches of the radial artery that enter dorsally near the waist and supply the bone in a retrograde fashion (from distal to proximal). Therefore, fractures occurring at the waist or proximal pole disrupt the blood supply to the proximal fragment, making the proximal pole highly susceptible to avascular necrosis and nonunion.

Reference: Gelberman RH, Menon J. The vascularity of the scaphoid bone. J Hand Surg Am. 1980;5(5):508-513.