When a child encounters a foreign organism (e.g., streptococcus) for the first time, he or she can respond with a humoral immune response specific for that organism. This is because of which of the following?

a. The antigens of the organism instruct unformed antibodies to take shape complementary to them.

b. The antigens of the organism stimulate clonal expansion of preexisting B cells with receptors specific for the antigens.

c. The organism is phagocytosed by macrophages and neutrophils.

d. The organism binds to pattern-recognition molecules on B cells.