**Core Concept**
Gonorrhoea is a sexually transmitted infection caused by the bacterium Neisseria gonorrhoeae. The diagnosis of gonorrhoea typically involves laboratory tests to detect the presence of the bacteria in various bodily fluids.

**Why the Correct Answer is Right**
The diagnosis of gonorrhoea is primarily based on the isolation of Neisseria gonorrhoeae from a patient's sample, such as urethral discharge, cervical swab, or other bodily fluids. The most common method is Gram staining, followed by culture on selective media, such as Thayer-Martin agar. The identification of the bacteria is confirmed through various biochemical tests, including sugar fermentation and oxidase assays.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option might refer to a rapid antigen test, but it is not the primary diagnostic method for gonorrhoea.
* **Option B:** This option might refer to a PCR (polymerase chain reaction) test, which is a sensitive method for detecting bacterial DNA, but it is not the standard diagnostic method for gonorrhoea.
* **Option D:** This option might refer to a clinical diagnosis based on symptoms, but gonorrhoea can be asymptomatic, making clinical diagnosis unreliable.

**Clinical Pearl / High-Yield Fact**
The Centers for Disease Control and Prevention (CDC) recommend dual therapy for gonorrhoea, consisting of a single dose of ceftriaxone and azithromycin, due to increasing antibiotic resistance.

**Correct Answer: C. Culture on Thayer-Martin agar.**