A diagnostic lateral flow assay is used to screen blood serum samples for the presence of prostate-specific antigen (PSA) using monoclonal antibodies.

The mechanics of the test strip are as follows:

• The sample is applied to the end of the strip and moves upwards via capillary action.
• The sample pad contains mobile, dye-conjugated monoclonal antibodies specific to PSA.
• The test zone ($T$) contains immobilized monoclonal antibodies that bind specifically to a different site on the PSA molecule.
• The control zone ($C$) contains immobilized antibodies that bind specifically to the mobile dye-conjugated antibodies to confirm successful fluid migration.

Which test strip represents a valid negative result, confirming that PSA is below the threshold of detection and that the assay has run correctly?