This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Neck, Subject name: Surgery
Which structure is preserved during modified radical neck dissection? 
Select and explain. 
A. Phrenic nerve, B. Submandibular gland, C. Sternocleidomastoid, D. Thoracic duct
C: Sternocleidomastoid
Answer: C: Sternocleidomastoid 
Explanation: Sternocleidomastoid muscle is preserved during modified radical neck dissection. Radical Neck Dissection Modified Radical Neck Dissection Removal of lymph nodes I-V + spinal accessory nerve + internal jugular vein + sternocleidomastoid muscleQ Removal of level I-V lymph nodes with (Mnemonic: SISm): Type I: preserves only Spinal accessory nerveQ Type II: preserves both spinal accessory nerve and Internal jugular veinQ Type III: preserves spinal accessory nerve, internal jugular vein and Sternocleidomastoid muscleQ(Functional neck dissectionQ)