The clonal selection theory states that

Options

A. an antigen selects certain B-cell and suppresses them
B. an antigen stimulates the multiplication of B-cells that produce antibodies against it
C. T-cells select those B-cells that should produce antibodies, regardless of antigens present
D. T-cells suppress all B-cells except the ones that should multiply and divide.

Answer

### Step-by-Step Solution:

1. **Understanding Clonal Selection Theory**: The clonal selection theory is a fundamental concept in immunology that explains how the immune system responds to specific antigens. It primarily focuses on B-cells, which are a type of lymphocyte.

2. **Pre-existing Lymphocytes**: The theory states that within a pre-existing group of lymphocytes (specifically B-cells), there are various specific cells that are capable of responding to different antigens.

3. **Activation by Antigen**: When a specific antigen enters the body, it selectively activates only those B-cells that have receptors specific to that antigen. This means that not all B-cells are activated, only those that can specifically bind to the antigen.

4. **Induction of Multiplication**: Once a specific B-cell is activated by its corresponding antigen, it induces that particular B-cell to multiply. This leads to the proliferation of that specific B-cell.

5. **Formation of Clones**: The activated B-cell then divides to produce identical clones of itself. These clones are all capable of producing the same antibody that is specific to the original antigen.

6. **Antibody Production**: The end result of this process is the production of a large number of identical B-cells, which can then produce antibodies against the specific antigen that triggered the response.

7. **Conclusion**: Therefore, the clonal selection theory essentially describes how an antigen stimulates the multiplication of specific B-cells, leading to the formation of clones that produce antibodies against that antigen.

### Correct Option:
The correct option based on the clonal selection theory is: **An antigen stimulates the multiplication of B-cells that produce antibodies against it.**

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