You skipped breakfast this morning and so haven't eaten for over 10 hours. as you sit here taking this exam, the major substrate for energy production in your brain is:

ketone bodies

Explanation:

In condition of hypoglycemia, the blood glucose and glycogen drops. Therefore ketone bodies  replaces glucose as  source of metabolite.

The ketone body is produced from the  beta oxidation of fatty acid in mitochondrial of the liver; to obtain Acetyl-Co enzyme A.The latter is used for the biosynthesis of Ketone bodies, which diffused across the blood-brain -barrier(BBB)  to the brain to act as metabolic substrate.Thus replacing glucose momentarily to sustain the brain.This result in elevated rise of blood ketone bodies concentration.

answer: hahahah its ok, its normal ; )