**Core Concept**
Microtubules are dynamic structures composed of tubulin proteins that play a crucial role in maintaining cellular shape, facilitating cell division, and enabling cell movement. They are a key component of the cytoskeleton, which is essential for maintaining cellular integrity and facilitating various cellular processes.

**Why the Correct Answer is Right**
Microtubules are responsible for maintaining cell shape by providing mechanical support and resisting external forces. They also enable cell motility by acting as tracks for motor proteins, such as kinesin and dynein, which move along the microtubules to propel the cell forward. The dynamic instability of microtubules allows for rapid changes in cell shape and movement. Microtubules are also involved in the formation of cilia and flagella, which are essential for cell motility in certain cell types.

**Why Each Wrong Option is Incorrect**

* **Option A:** Microfilaments, composed of actin proteins, are primarily involved in cell signaling, muscle contraction, and maintaining cellular shape, but they are not as crucial for cell motility as microtubules.
* **Option C:** The Golgi apparatus is a complex organelle involved in protein modification, sorting, and packaging, but it does not contribute to cell shape or motility.
* **Option D:** Mitochondria are the primary site of cellular energy production and are not directly involved in maintaining cell shape or facilitating cell movement.

**Clinical Pearl / High-Yield Fact**
The microtubule network is dynamic and can be rapidly reorganized in response to changes in cellular needs, such as during cell division or movement.

**✓ Correct Answer: B. Microtubules**