antibodies that are passed on from mother to child are part of passive immunity. Passive immunity antibodies come from another source and are only temporary.
Answer: The correct answer for the full in the blank is "Passive immunity".
Passive immunity is the transfer of active humoral response (with ready made antibodies) into the individual.
It can be naturally acquired by mother during gestation period (where antibody from mother is transferred to fetus via placenta) and through breast feeding (antibody transferred through breast milk).
Thus, antibodies transferred to child from mother are part of Passive immunity.
