**Core Concept**
The vaginal sphincter, also known as the external anal sphincter in the context of the anal canal but referring here to the muscles surrounding the vagina, is composed of muscles that provide support and maintain continence. The main muscles involved are part of the **pelvic floor**. The primary muscles forming the vaginal sphincter mechanism include the **bulbospongiosus**, **superficial transverse perinei**, and **external anal sphincter** indirectly, as it surrounds the anus adjacent to the vagina.

**Why the Correct Answer is Right**
Given the options are missing, we'll discuss the general composition. The **bulbospongiosus muscle** plays a key role in covering and compressing the vagina, aiding in the sphincter mechanism. However, without the specific options, we focus on the typical components. The correct answer would involve identifying a muscle not primarily involved in the formation of the vaginal sphincter.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific option provided, we cannot directly address why it's incorrect. Normally, we'd discuss how each listed muscle does or doesn't contribute to the vaginal sphincter mechanism.
**Option B:** Similarly, without details, we can't specify why this option is incorrect, but typically, we'd explain the role or lack thereof of the listed muscle in sphincter formation.
**Option C:** This option's incorrectness would depend on its identity and role in pelvic floor anatomy.
**Option D:** The explanation for its incorrectness would hinge on understanding which muscle is listed and its relation to the vaginal sphincter.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the **pelvic floor muscles**, including those forming the vaginal sphincter, play a crucial role in **urinary and fecal continence**, as well as **sexual function**. Damage to these muscles, such as during childbirth, can lead to significant clinical issues.

**Correct Answer:** Correct Answer: D. Levator ani