Functions and Differentiation of Lymphocytes Steps:

• Statement 1 is correct: Upon activation, some B cells differentiate into memory B cells, and some T cells into memory T cells, enabling faster responses to future infections.
• Statement 2 is incorrect: Individual B-lymphocytes produce antibodies specific to one antigen; multiple types arise from different B cell clones, not a single cell.
• Statement 3 is correct: Plasma cells, derived from activated B-lymphocytes, specialize in secreting large amounts of antibodies directly into the blood plasma.
• Statement 4 is incorrect: Helper T cells activate macrophages to destroy engulfed pathogens, but "kill cells" inaccurately suggests killing host cells, a function of cytotoxic T cells.

Why B is correct:

• It selects only the accurate statements (1 and 3), based on standard immunology definitions of cell differentiation and antibody production.

Why the others are wrong:

• A includes the false statement 2 about antibody diversity.
• C includes the false statement 2 and excludes correct 1 and 3.
• D includes the false statement 2 and excludes correct 1.

Final answer: B