"Rely" vs. "Relies" usage

  1. The subjective nature of these tests rely on human expertise to assess the patient correctly

  2. The subjective nature of these tests relies on human expertise to assess the patient correctly

Which is correct to say, and why?


Solution 1:

The subject of the sentence is "the subjective nature (of these tests)". Therefore "rely" is inflected in agreement with "nature", which is singular.

Thus the only correct one is

The subjective nature of these tests relies on human expertise to assess the patient correctly