You are presented with the quiz "What lasts only as long as the proteins that attach to an antigen survive in body fluids?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "passive immunity lasts only as long as the antibodies survive in body fluids" and "an antibody is a protein that attaches to an antigen". 

So, what's the best answer to the question?


 

        passive immunity   