In such a test, HCG antigen would be attached to beads, and monoclonal antibodies would normally causes the beads to agglutinate. However, high levels of HCG in a test sample would prevent agglutination since the sample's HCG would overwhelm and prevent binding of the antibodies. This would show up as some kind of visible result for reading the test.
Work Step by Step
The key here is to just read the text, especially the caption for Fig. 51.21, and apply that generalized example to the specific case of a test for HCG.