## **Core Concept**
The question tests the understanding of how different substances are absorbed in the gut, focusing on the mechanisms of absorption. In the gastrointestinal tract, substances can be absorbed through active transport, passive diffusion, facilitated diffusion, or endocytosis. Passive absorption, specifically, involves the movement of substances across the intestinal wall without the need for energy input.

## **Why the Correct Answer is Right**
Alcohol (ethanol) is passively absorbed in the gut. This is because alcohol can diffuse directly through the cell membranes of the intestinal epithelial cells. The absorption of alcohol is not dependent on active transport mechanisms; instead, it moves down its concentration gradient. This passive diffusion allows alcohol to be quickly absorbed into the bloodstream, which is why it can act rapidly after ingestion.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Glucose is primarily absorbed through active transport in the gut. It is co-transported with sodium ions into the intestinal epithelial cells via the sodium-glucose cotransporter 1 (SGLT1), which requires energy indirectly by using the sodium gradient maintained by the Na+/K+ ATPase pump.
- **Option B:** Certain nutrients like amino acids are also absorbed through active transport mechanisms. They can be absorbed via cotransport with sodium ions or through other facilitated diffusion mechanisms but not through passive absorption like alcohol.
- **Option D:** Fatty acids are absorbed through a more complex process involving their solubilization by bile salts, uptake into intestinal cells, re-esterification into triglycerides, and packaging into chylomicrons for transport.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that alcohol can be absorbed rapidly in the stomach and small intestine, but its absorption can be slowed by food, particularly fatty foods, which delay gastric emptying. This is a clinically relevant fact because it influences how quickly alcohol can exert its effects and potentially lead to toxicity.

## **Correct Answer:** C. Alcohol.