A set <span>is a group of consecutive repetitions.</span>
Really, none of these answers are good. leukocytes are the body's general immune cell, and lymphocytes are a type of leukocyte. Antibodies are only used when fighting an infection that your body already has experience with, so I'm guessing it you have to pick from these answers, its "lymphocytes", but it's not really the best answer.
Maslow’s hierarchy of needs
The action of leading a group of people or an organization
