The antibodies that activate the complement system are

The antibodies that activate the complement system are
 
  a. IgA and IgD.
  b. IgG and IgM.
  c. IgG and IgD.
  d. IgE and IgM.
  e. IgA and IgE.

Question 2

Consider two IgG molecules, each of which reacts with a different epitope. Which of the following
  statement(s) is(are) TRUE?
 
  a. They will have the same amino acid sequence in their constant regions.
  b. They will have different amino acid sequences in their variable regions.
  c. They can bind the same antigen.
  d. They can bind different antigens.
  e. They can bind the same antibody.