The Complement Fixation Test Uses Red Blood Cells as the Target

The complement fixation test uses red blood cells as the target for complement activation. Test serum containing antibodies is combined with a known amount of antigen in a tube, and then the RBCs and antibodies against the RBCs are added. A positive result for the complement fixation test would be

A) a line of precipitate near the bottom of the tube.
B) a cloudy solution in the tube.
C) a solution that is clear due to precipitation of RBCs.
D) a fluorescent precipitate.
E) loss of color in the tube.