## **Core Concept**
Aldosugars are a type of monosaccharide that contains an aldehyde functional group. They are significant in carbohydrate chemistry and are classified based on the number of carbon atoms and the presence of the aldehyde group.

## **Why the Correct Answer is Right**
The correct answer, **D. Glucose**, is an aldosugar because it has an aldehyde group at one end of its carbon chain. Glucose is a hexose (six-carbon sugar) and exists primarily in its cyclic form but can open up to reveal an aldehyde group, making it an aldosugar. This characteristic is crucial for its identification and differentiation from ketosugars, which have a ketone group.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, without the specific structure provided, we cannot directly assess its classification. However, if it's not an aldosugar, it could either be a ketosugar or not a monosaccharide.
- **Option B:** This option is incorrect if the structure represents a ketosugar or a different type of sugar that does not contain an aldehyde group.
- **Option C:** Similarly, this option is incorrect if it does not represent a sugar with an aldehyde group.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that glucose is a primary aldosugar used by cells for energy. The presence of an aldehyde group in aldosugars like glucose is critical for certain chemical reactions, including the Benedict's test, which is used to detect reducing sugars.

## **Correct Answer:** **D. Glucose**