Ketone bodies are formed from

The correct option is Acetyl CoA.

Ketone bodies (acetoacetate, $\beta$-hydroxybutyrate, and acetone) are water-soluble molecules containing the ketone group that are produced by the liver from fatty acids during periods of low food intake (fasting), carbohydrate-restrictive diets, starvation, prolonged intense exercise, or in untreated type 1 diabetes mellitus.

The synthesis of ketone bodies, a process known as ketogenesis, occurs primarily in the mitochondria of liver cells (hepatocytes). The biochemical pathway begins with the breakdown of fatty acids via $\beta$-oxidation, which yields acetyl coenzyme A (acetyl CoA).
When the body's glucose levels are low, oxaloacetate is diverted from the citric acid cycle (Tricarboxylic Acid Cycle) to be used in gluconeogenesis to generate glucose. Because oxaloacetate is depleted, acetyl CoA cannot condense with it to enter the citric acid cycle.
Instead, excess acetyl CoA molecules are diverted into the ketogenesis pathway:
1. Two molecules of acetyl CoA condense to form acetoacetyl CoA, catalyzed by the enzyme thiolase.
2. Acetoacetyl CoA condenses with another acetyl CoA to form 3-hydroxy-3-methylglutaryl CoA (HMG-CoA), catalyzed by HMG-CoA synthase.
3. HMG-CoA is then cleaved by HMG-CoA lyase to yield acetoacetate (a ketone body) and acetyl CoA.
4. Acetoacetate can then be reduced to $\beta$-hydroxybutyrate or spontaneously decarboxylated to form acetone.

Therefore, the precursor molecule from which all ketone bodies are synthesized is acetyl CoA.