An epitope is the part of the antigen that binds to the antibody i.e they are the antigenic determinants present in an antigen. The part of the antibodies to which the antigen binds is known as the paratope i.e it is the antigen binding site on an antibody. A proto-oncogene is an inactive cancer gene. It is a normal gene that would become a cancer-causing gene on mutation or over-expression in the cells. Metastasis is the spread of cancer from its primary site to other regions in the body. So, the correct options are ' A-2, B-5, C-4, D-1'.