## Core Concept
Intermediate filaments are a component of the cytoskeleton in cells, providing mechanical support and stability. They are crucial for maintaining cell shape and are involved in the structural integrity of tissues. Intermediate filaments are particularly important in cells that experience mechanical stress.

## Why the Correct Answer is Right
The correct answer, **D. Tumor markers**, relates to the use of certain intermediate filaments in diagnostic pathology. For example, cytokeratins (a type of intermediate filament found in epithelial cells) and vimentin (found in mesenchymal cells) are used as markers to identify the origin of tumors. This is because the expression of specific intermediate filaments can help in determining the cell type from which a tumor originates.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because, although intermediate filaments do provide structural support, the term is too broad and does not specifically relate to a common use like tumor markers.
- **Option B:** This option is incorrect as it does not accurately reflect a recognized application of intermediate filaments.
- **Option C:** This option is incorrect because, while the cytoskeleton (which includes intermediate filaments) is involved in cell division, this option does not accurately represent a specific use of intermediate filaments like tumor markers do.

## Clinical Pearl / High-Yield Fact
A key point to remember is that certain types of intermediate filaments are used as tumor markers. For instance, **cytokeratin 7 (CK7) and cytokeratin 20 (CK20)** are used to help differentiate between various types of carcinomas based on their cytokeratin expression profiles. This can be crucial in identifying the primary site of metastatic cancers.

## Correct Answer Line
**Correct Answer: D. Tumor markers.**