**Core Concept**
The question is testing the student's ability to diagnose a condition based on symptoms, specifically the association between greenish vaginal discharge and severe itching. This symptomatology is suggestive of a specific infectious or inflammatory condition affecting the female genital tract.

**Why the Correct Answer is Right**
The greenish vaginal discharge is indicative of a Trichomonas vaginalis infection, also known as trichomoniasis. This parasitic infection is caused by the protozoan Trichomonas vaginalis, which is transmitted through sexual contact. The severe itching is a result of the inflammatory response to the infection. The discharge is typically greenish or yellowish in color, frothy, and has a strong, unpleasant odor.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because bacterial vaginosis (BV) typically presents with a thin, white, or gray discharge with a fishy odor, not greenish in color.

**Option B:** This option is incorrect because candidiasis, a fungal infection, typically presents with a thick, white, cottage cheese-like discharge, not greenish in color.

**Option C:** This option is incorrect because gonococcal infection typically presents with a purulent discharge, often accompanied by pelvic pain and other systemic symptoms.

**Clinical Pearl / High-Yield Fact**
Remember that Trichomonas vaginalis infection is a common sexually transmitted infection that can be diagnosed with a wet mount microscopy of the vaginal discharge, showing the characteristic motile protozoa.

**Correct Answer: C. Trichomonas vaginalis infection.**