How do antibodies make antigens useless?
a. by attaching to them
b. by dissolving them
c. by covering them with carbon dioxide
d. by hiding them

A) This process is called "Neutralisation" and can lead to Opsonisation. Its basically the process where antigens bind and surround the antigen in like a mesh. Much like wrapping lots of paper around a ball

The reasons the antibody binds only to the antigen is that the structure of the antibody has a "head" with a composition that only bonds to the antigen

Plasma with a clotting factor removed.