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 explains how the immune system responds to specific antigens. It primarily focuses on B-cells, which are a type of lymphocyte involved in the adaptive immune response.

2. **Activation of B-cells**: When an antigen enters the body, it binds to specific B-cells that have receptors for that particular antigen. This binding is crucial as it activates the B-cells.

3. **Clonal Expansion**: Once the B-cells are activated by the antigen, they undergo clonal expansion. This means that the activated B-cells multiply to form clones of themselves.

4. **Production of Antibodies**: The clones of B-cells are responsible for producing antibodies. These antibodies are specific to the antigen that triggered the activation of the B-cells.

5. **Monospecific Antibodies**: The antibodies produced by the clones are termed monospecific antibodies, meaning they are specific to a single type of antigen.

6. **Evaluating Options**: The question provides several options regarding the clonal selection theory. We need to identify the correct statement based on our understanding:
- Option 1: Incorrect, as it mentions suppression, which does not occur.
- Option 2: Correct, as it accurately describes the activation and multiplication of B-cells leading to antibody production.
- Option 3: Incorrect, as T-cells do not select B-cells regardless of the antigen.
- Option 4: Incorrect, as it also mentions suppression, which is not part of the clonal selection process.

7. **Conclusion**: The correct answer is that an antigen stimulates the multiplication of B-cells, which then produce antibodies against it.