This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Muscles of arm and forearm region & Cubital fossa, Subject name: Anatomy
[{'content': 'Mallet finger is a flexion deformity of the distal phalanx, which occurs due to \nSelect and explain. \nA. Avulsion fracture of middle phalanx, B. Rupture of collateral slips of extensor expansion, C. Rupture of central slip of extensor expansion, D. Dislocation of distal interphalangeal joint', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Mallet finger is a flexion deformity of the distal phalanx due to injury to the extensor digitorum at its inseion to the base of the distal phalanx (the collateral slips).', 'role': 'assistant'}]