This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Physiology
Which of the following is considered as a marker for epididymal function? 
Select and explain. 
A. Fructose, B. Testosterone, C. Acid phosphatase, D. Carnitine
D: Carnitine
Answer: D: Carnitine 
Explanation: In the epididymis, the columnar cells that, with the basal cells, form the majority of the epithelium. These cells extend from the lumen to the basal lamina, They also have non-motile stereocilia, which are long and branching in the head region and shoer in the tail region. They also secrete carnitine, sialic acid, glycoproteins, and glycerylphosphorylcholine into the lumen.Ref: Ganong&;s review of medical physiology; 24th edition; page no: 419