Antibodies transferred across the placenta to protect the fetus illustrate which type of adaptive immunity?

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This scenario is about passive immunity, where the recipient gains antibodies without making them in response to an antigen. When maternal antibodies cross the placenta, the fetus receives those antibodies directly from the mother, so the fetus isn’t mounting its own immune response. Because this transfer happens naturally during pregnancy, it’s naturally acquired. It’s also temporary, since the maternal antibodies decline over time and no lasting immune memory is established in the fetus. In contrast, active immunity would involve the fetus producing its own antibodies and memory cells after infection or vaccination, and artificial immunity would come from medical interventions rather than natural maternal transfer.