**Core Concept**
Intermediate filaments are a type of cytoskeletal structure found in eukaryotic cells, playing a crucial role in maintaining cell shape, providing mechanical support, and protecting against mechanical stress. They are composed of various proteins, including keratins, vimentin, lamin, and neurofilaments, which are specific to different cell types.

**Why the Correct Answer is Right**
Intermediate filaments are characterized by their resistance to extraction with non-ionic detergents, unlike microtubules and actin filaments. They are involved in maintaining cell shape, particularly in epithelial cells, where they form a network to provide structural support. The main types of intermediate filaments are:
- Keratins: present in epithelial cells
- Vimentin: present in mesenchymal cells
- Lamin: present in the nuclear lamina
- Neurofilaments: present in neurons

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as keratins are indeed intermediate filaments, specifically type I and type II keratins, which are co-expressed in epithelial cells to form a heteropolymer.
**Option B:** This option is incorrect as vimentin is an intermediate filament protein, specifically expressed in mesenchymal cells and involved in cell adhesion and migration.
**Option C:** This option is incorrect as neurofilaments are intermediate filaments, specifically expressed in neurons and involved in maintaining axonal structure and stability.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that intermediate filaments are not extractable with non-ionic detergents, unlike microtubules and actin filaments. This characteristic is crucial for distinguishing intermediate filaments from other cytoskeletal structures.

**Correct Answer:** D