**Core Concept**
The complementarity-determining regions (CDRs) are a crucial part of antibodies that determine their specificity and ability to bind to antigens. These regions are responsible for recognizing and interacting with specific epitopes on the surface of antigens, facilitating the immune response.

**Why the Correct Answer is Right**
The CDRs are highly variable and are encoded by the variable (V) gene segments of the immunoglobulin genes. They are characterized by their high degree of diversity and are responsible for the unique specificity of each antibody. The CDRs are composed of three loops in the heavy chain and three loops in the light chain, which form the binding site for the antigen. The CDRs interact with the antigen through weak non-covalent interactions, such as hydrogen bonding, ionic interactions, and van der Waals forces.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the framework regions (FRs) are the conserved parts of the antibody that provide structural support to the CDRs, but they are not responsible for antigen recognition.
**Option B:** This option is incorrect because the constant (C) region is the part of the antibody that is constant across different antibodies and provides effector functions, such as complement activation and antibody-dependent cellular cytotoxicity.
**Option C:** This option is incorrect because the hypervariable regions are another term for the complementarity-determining regions (CDRs), but it is not the most commonly used term in immunology.

**Clinical Pearl / High-Yield Fact**
The CDRs are responsible for the specificity and efficacy of antibodies, making them a crucial target for the development of therapeutic antibodies. Understanding the structure and function of the CDRs is essential for the design of antibodies that can target specific diseases.

**Correct Answer: C. Complementarity-determining regions (CDRs) are the highly variable regions of antibodies responsible for antigen recognition and specificity.**