Complement is a series of impoant host proteins which provide protection from invasion by foreign microorganisms. Which one of the following statements best describes complement?

Both IgG and IgM activate complement by the classic pathway, while IgA activates it by the alternative pathway. Neither IgD nor IgE can activate complement. Complement is a system of several proteins that is activated by either an immune or a nonimmune pathway. Both of these pathways result in the production of many biologically active components that cause cell lysis and death. Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition