What is (are) the role(s) of complement proteins in the immune response?I. They attract white blood cells to the site of infection. II. They help other cells avoid infection. III. They cause pathogens to clump together, making the pathogens easier to identify and destroy. IV. They form a pore in the plasma membrane of a pathogen, causing it to rupture.

Complement protein C5a attracts white blood cells to an infection site, so statement I is correct. Other complement proteins assemble into the membrane attack complex, which forms pores in pathogen membranes and can make them rupture, so IV is correct. Helping host cells avoid infection and causing pathogens to clump are not the roles described here; clumping is mainly associated with antibodies.

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