What Is the Principle of the Flocculation Test

What is the principle of the flocculation test?

A) The antigen is incorporated into the agar and the test wells hold the antibody. The antibody and antigen combine at a specific concentration and produce a zone of equivalence.
B) Antibodies are mixed with a labeled antigen, and a sandwich reaction occurs.
C) Antibodies and antigens combine then precipitate out of a solution to the bottom of the tube.
D) The antigen-antibody reaction forms a macroscopically visible clump that remains in solution.