**Core Concept**
The Paul-Bunnell test, also known as the Paul-Bunnell reaction, is a serological test used to diagnose infectious mononucleosis, a disease caused by the Epstein-Barr virus (EBV).

**Why the Correct Answer is Right**
The Paul-Bunnell test detects the presence of heterophile antibodies in the serum of patients with infectious mononucleosis. These antibodies are produced in response to the EBV infection and react with the sheep red blood cells (SRBCs) used in the test, causing agglutination. The test is based on the principle of heterophile antibody detection, which involves the reaction between the antibodies produced in response to the EBV infection and the SRBCs.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the Paul-Bunnell test is not a type of complement fixation test.
**Option B:** This option is incorrect because the Paul-Bunnell test is not a type of precipitation reaction.
**Option C:** This option is incorrect because the Paul-Bunnell test is not a type of immunofluorescence test.

**Clinical Pearl / High-Yield Fact**
The Paul-Bunnell test is a classic example of a heterophile antibody test, which detects antibodies that react with antigens from a different species. This concept is crucial in understanding the pathophysiology of infectious mononucleosis and the diagnostic tests used to diagnose the disease.

**Correct Answer:** C. Type of heterophile antibody test.