One of the most remarkable aspects of the human immune system is its diversity, that is, the ability to recognize a wide range of antigens and to mount a specific antibody response. This is called clonal selection. At the cellular level, which of the following are primarily responsible for such specificity?

**Core Concept**
The **clonal selection theory** is a fundamental principle in immunology that explains how the immune system can recognize and respond to a vast array of antigens. This theory is based on the concept of **antigen-specific recognition** by immune cells. The immune system's ability to mount a specific response is largely due to the diversity of **B cells** and **T cells**.

**Why the Correct Answer is Right**
Although the correct answer is not provided, the correct answer should be **B cells**, as they are primarily responsible for the specificity of the immune response through the production of **antibodies**. Each B cell expresses a unique **antibody** on its surface, which recognizes a specific **antigen**. When a B cell encounters its corresponding antigen, it becomes activated and proliferates, giving rise to a clone of cells that produce the same antibody.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not provided.
**Option C:** This option is incorrect because it is not provided.
**Option D:** This option is incorrect because it is not provided.

**Clinical Pearl / High-Yield Fact**
The clonal selection theory has important implications for our understanding of immune function and **vaccine development**. A key concept to remember is that each B cell is specific to a particular antigen, allowing for a targeted response to infection.

**Correct Answer:** Not provided, however, the most likely correct answer is B cells.

✓ Correct Answer: B. Hypervariable regions in domains of B cells