This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Marker for biliary tract obstruction - 
Select and explain. 
A. Alkaline phosphatase, B. Aspaate transaminase, C. Alanine transaminase, D. Creatinine kinase
A: Alkaline phosphatase
Answer: A: Alkaline phosphatase 
Explanation: Answer-A. Alkaline phosphataseEnzymes that reflect cholestasisAlkaline phosphatase5'- nucleotidaseGamma-glutamyl transpeptidase (GGT)Lipoprotein-X is an abnormal lipoprotein that appears in the sera of patients with obstructive jaundice and thus is a sensitive indicator of cholestasis.