This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Upper limb, Subject name: Anatomy
Axillary sheath is derived from 
Select and explain. 
A. Preveebral fascia, B. Pretracheal fascia, C. Investing layer of deep cervical fascia, D. Deep fascia of throacic wall
A: Preveebral fascia
Answer: A: Preveebral fascia 
Explanation: -The muscular floor of the posterior triangle is covered by preveebral layer of fascia colli. -It forms the axillary sheath around subclan aery and brachial plexus travelling from the root of neck to the upper limb. -reference: Textbook of anatomy, Head Neck, and brain, Vishram Singh, 2nd edition, page no.80