**Core Concept**
The presence of a greenish discharge per vaginum suggests an infection that involves the breakdown of hemoglobin, leading to the production of biliverdin and biliverdin reduction to bilirubin, which imparts a greenish color to the discharge.

**Why the Correct Answer is Right**
The greenish discharge is typically associated with Trichomonas vaginalis infection. This protozoan parasite causes an inflammatory response in the vagina, leading to the release of lysosomal enzymes that break down hemoglobin, resulting in the production of biliverdin and the characteristic greenish color of the discharge. The infection also causes a significant increase in the production of prostaglandins, leading to the symptoms of vaginitis, such as itching, burning, and a frothy, greenish-yellow discharge.

**Why Each Wrong Option is Incorrect**
**Option A:** Candida albicans infection typically presents with a thick, white, cottage cheese-like discharge, not a greenish discharge.
**Option B:** Bacterial vaginosis (BV) is characterized by a thin, white or gray discharge with a fishy odor, not a greenish discharge.
**Option C:** Chlamydia trachomatis infection typically presents with a mucopurulent discharge, not a greenish discharge.

**Clinical Pearl / High-Yield Fact**
Remember that Trichomonas vaginalis infection is often associated with a characteristic "strawberry" appearance of the cervix on examination, due to the presence of punctate hemorrhages.

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