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: Biochemistry
The main source of energy derived from 
Select and explain. 
A. Fat, B. Glycogen, C. Lactate, D. Acetone
B: Glycogen
Answer: B: Glycogen 
Explanation: Liver glycogen is the first main provider of energy during short term fasting.
Liver glycogen serves to maintain blood glucose between the meals. Therefore, liver glycogen is the most important reservoir as it comes to play its role in routine condition (between meals). Whereas, adipose tissue fuel is involved only on prolonged fasting and starvation.