Final answer:
Clonal anergy is a state of unresponsiveness, where B cells become nonfunctional when they react to soluble antigens in the bone marrow, forming part of the immune system's tolerance mechanisms.
Step-by-step explanation:
Clonal anergy refers to a state where immune cells, particularly B cells, become nonresponsive to an antigen stimulation. This process occurs when B cells that react to soluble antigens in the bone marrow are made nonfunctional.
Instead of being physically deleted like in clonal deletion, these cells become unable to mount an immune response. The state of clonal anergy is an important part of the immune system's mechanism to prevent autoimmune diseases by ensuring that self-reactive B cells that escape central tolerance in the bone marrow do not cause harm to the body. So, the correct answer to the student's question is 'B. unresponsiveness.'