This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Peripheral nerve injuries, Subject name: Anatomy
A patient can extend his wrist6 but cannot extend Metacarpophalyngeal joint of hand after he has met with an accident. Sensations in the limb are normal. Level at WhiCh the affected nerve is injured 
Select and explain. 
A. At coracobrachialis, B. Head of radius, C. Spiral groove, D. Surgical neck of humerus.
B: Head of radius
Answer: B: Head of radius 
Explanation: Normal sensation band normal wrist extension with inability to extend MCP joints suggest the diagnosis of PIN injury Most common of injury is around radial head and neck Refer Apleys 9th/e p 282