This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory Chain, Subject name: Biochemistry
What is the principle of the given test for Urine reducing substance? 
Select and explain. 
A. Cu2+ ions are reduced to Cu+ ions by enediols, B. Cu+ ions are oxidised to Cu2+ ions by enediols, C. Fe2+ ions are reduced to Fe+ ions by enediols, D. Fe+ ions re oxidised to Fe2+ ions by enediols
A: Cu2+ ions are reduced to Cu+ ions by enediols
Answer: A: Cu2+ ions are reduced to Cu+ ions by enediols 
Explanation: Ans. A. Cu2+ ions are reduced to Cu+ ions by enediols* This test is Benedicts test. The principle of the test is*Cu2+ions present in Copper sulphate is reduced to Cuprous hydroxide and later to Cuprous oxide by enediols formed from reducing sugar