This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thorax, Subject name: Anatomy
Which of the following duct commences in the abdomen as an elongated lymph sac of the cisterna chyli is? 
Select and explain. 
A. Thoracic duct, B. Ganer's duct, C. Bile duct, D. Hepatic duct
A: Thoracic duct
Answer: A: Thoracic duct 
Explanation: The thoracic duct is the largest lymphatic vessel in the body.It extends from the upper pa of the abdomen to the lower pa of the neck,crossing the posterior and superior pas of the mediastinum.It is about 45 cm long.It has a beaded appearance because of the presence of many valves in its lumen. It begins as a continuation of the upper end of cisterna chyli near the lower border of the twelth thoracic veebra and enters the thorax through the aoic opening of the diaphragm. <img src=" /> REF.B D Chaurasia's human anatomy vol.1,fifth edition.pg 270