In immune response mechanism clonal selection is a process in which

The correct option is B
the proliferation and differentiation of lymphocytes occur in response to a specific antigen
Clonal selection is a process proposed to explain how a single B or T cell that recognizes an antigen that enters the body is selected from the pre-existing cell pool of differing antigen specificities and then reproduced to generate a clonal cell population that eliminates the antigen.

During clonal selection, random mutations during clonal expansion cause the production of B cells with increased antibody-binding affinity for their antigens.

When an antigen encounters the immune system, its epitopes eventually will react only with B-lymphocytes with B-cell receptors on their surface that more or less fit and this activates those B-lymphocytes. This process is known as clonal selection.

Clonal selection is the theory that specific antigen receptors exist on lymphocytes before they are presented with an antigen due to random mutations during initial maturation and proliferation. After antigen presentation, selected lymphocytes undergo clonal expansion because they have the needed antigen receptor.

Therefore, the correct answer is "option b".