**Core Concept**
Stem cells are a class of undifferentiated cells that have the ability to differentiate into various cell types, contributing to tissue repair, growth, and regeneration. This unique property allows them to self-renew and maintain a stable population, while also giving rise to specialized cells that perform specific functions within the body.

**Why the Correct Answer is Right**
Stem cells utilize a complex interplay of signaling pathways and transcription factors to regulate their self-renewal and differentiation potential. Key players in this process include the Wnt/β-catenin and Notch signaling pathways, as well as transcription factors such as Oct4 and Sox2. These molecules work together to maintain the balance between stem cell self-renewal and differentiation, enabling them to respond to tissue damage and developmental cues.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is vague and does not accurately capture the unique properties of stem cells. Stem cells are more than just cells with the ability to grow and proliferate.
**Option B:** This option is incorrect because stem cells are not simply a type of cell that can be replaced or regenerated. Their ability to differentiate into various cell types sets them apart from other cell types.
**Option C:** This option is not accurate because stem cells are not solely responsible for tissue repair and regeneration. While they do play a crucial role in these processes, other cell types and mechanisms also contribute to tissue maintenance and repair.

**Clinical Pearl / High-Yield Fact**
It's essential to note that stem cells can be isolated from various tissues, including bone marrow, adipose tissue, and umbilical cord blood. These sources are used in regenerative medicine and tissue engineering applications.

**Correct Answer: C. Cells that can differentiate into various cell types.**