Final answer:
Gamma globulins are plasma proteins that act as antibodies, which are crucial in the body's immune response, and are produced by plasma cells.
Step-by-step explanation:
Plasma proteins that function as antibodies and attack foreign proteins are classified as gamma globulins. These proteins are involved in immunity and are also known as immunoglobulins or antibodies. Gamma globulins are produced by specialized B lymphocytes called plasma cells, and they play a critical role in protecting the body by binding to foreign objects such as bacteria and viruses. Therefore, the correct answer to the question is C. gamma globulins.