**Core Concept**
Carbohydrate malabsorption can be assessed using various breath tests that measure the production of volatile organic compounds (VOCs) in the gut. These tests take advantage of the fact that certain bacteria in the gut ferment undigested carbohydrates, producing gases such as hydrogen, methane, and carbon dioxide.

**Why the Correct Answer is Right**
The correct answer is hydrogen breath test (HBT). HBT measures the amount of hydrogen gas in the breath after ingestion of a carbohydrate source, such as lactose or fructose. This is based on the principle that when undigested carbohydrates reach the colon, they are fermented by bacteria, producing hydrogen gas as a byproduct. The hydrogen gas is then absorbed into the bloodstream and exhaled in the breath. Elevated levels of hydrogen in the breath indicate carbohydrate malabsorption.

**Why Each Wrong Option is Incorrect**
**Option A:** Stool tests, such as the lactose tolerance test, can be used to assess carbohydrate malabsorption, but they are not as sensitive or specific as breath tests like HBT. Stool tests measure the amount of undigested carbohydrate in the stool, but they can be influenced by factors such as gut motility and bacterial overgrowth.
**Option B:** Glucose tolerance tests are used to assess glucose metabolism, not carbohydrate malabsorption. While glucose tolerance tests can provide information on insulin sensitivity and glucose uptake, they do not directly assess carbohydrate malabsorption.
**Option C:** Gastric emptying studies are used to assess the rate at which the stomach empties its contents into the small intestine, but they do not directly assess carbohydrate malabsorption.

**Clinical Pearl / High-Yield Fact**
The hydrogen breath test is a non-invasive, easily administered test that can be used to diagnose carbohydrate malabsorption in a variety of conditions, including lactose intolerance, fructose malabsorption, and small intestine bacterial overgrowth (SIBO).

**Correct Answer:** C. Hydrogen breath test