## **Core Concept**
The question pertains to the structural isomers of glucose, specifically focusing on the differences in the position of -H and -OH groups at the 2nd, 3rd, and 4th carbon atoms. This concept falls under stereochemistry and carbohydrate chemistry.

## **Why the Correct Answer is Right**
The correct answer, **C. Epimers**, is right because epimers are carbohydrates that differ in configuration at only one carbon atom. However, when considering the broader context of the question, which seems to hint at a group of isomers differing at more than one carbon (2nd, 3rd, and 4th), it seems there might be a bit of confusion. Typically, glucose's stereoisomers that differ at multiple carbons are considered in the context of aldohexoses. The aldohexoses include glucose, mannose, and galactose, among others, which are indeed different in the position of -H and -OH at various carbon atoms.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option seems to be missing text, but typically, if it referred to a specific type of isomer or carbohydrate, it would be incorrect if it didn't accurately describe isomers differing by the position of -H and -OH groups at multiple carbons.
- **Option B:** Similar to Option A, without specific text, it's hard to directly refute, but if it suggested another form of isomerism (like enantiomers, which differ at all chiral centers), it would be incorrect in this context.
- **Option D:** Again, without text, assuming it suggests a form of isomerism not applicable to the description given (like tautomers or not relevant to carbohydrate chemistry), it would be incorrect.

## **Clinical Pearl / High-Yield Fact**
A memorable point for exams is that **epimers** differ at one carbon, a classic example being glucose and galactose, which are epimers at C-4. Understanding the basic structures and differences between aldohexoses (like glucose, mannose, and galactose) can help in quickly identifying types of isomerism in carbohydrates.

## **Correct Answer:** C. Epimers