D
Antibodies are produced for a specific type of antigen and can only lock onto that one.
Reasoning for each answer:
A) White Blood Cells engulf and destroy pathogens.
B) An antigen is a toxic or foreign substance that causes the immune system to respond.
C) Producing immature cells wouldn't work as they aren't fulling developed.
D) Antibodies are produced for a specific type of antigen and can only lock onto that one.