**Core Concept**
The skeletal framework of a cell, also known as the cytoskeleton, is composed of three main components: microtubules, microfilaments, and intermediate filaments. Microtubules are dynamic structures that play a crucial role in maintaining cell shape, providing mechanical support, and facilitating intracellular transport.

**Why the Correct Answer is Right**
Microtubules are composed of tubulin subunits and are stabilized by microtubule-associated proteins (MAPs). They form a network of filaments that provide structural support to the cell, maintaining its shape and allowing for cell division and movement. Microtubules also serve as tracks for motor proteins, such as kinesin and dynein, which transport vesicles and organelles throughout the cell.

**Why Each Wrong Option is Incorrect**
**Option A:** The nucleus is the control center of the cell, containing the genetic material, but it does not provide structural support to the cell.
**Option C:** Ribosomes are responsible for protein synthesis, not providing structural support to the cell.
**Option D:** Mitochondria are the site of cellular respiration and energy production, but they do not contribute to the skeletal framework of the cell.

**Clinical Pearl / High-Yield Fact**
The cytoskeleton is dynamic and constantly remodeling itself in response to changes in cell shape and mechanical stress. Disruption of the cytoskeleton has been implicated in various diseases, including cancer, neurodegenerative disorders, and muscular dystrophy.

**✓ Correct Answer: B. Microtubules**