**Core Concept**
The underlying condition being tested is likely anorectal malformation or **imperforate anus**, a congenital anomaly where the rectum is malformed and not connected to the anus. This condition often presents with an inability to pass meconium and may involve other associated anomalies.

**Why the Correct Answer is Right**
Since the correct answer is not explicitly provided, let's discuss the general approach to diagnosing anorectal malformations. The investigation of choice typically involves imaging studies to assess the anatomy of the rectum and anus.

**Why Each Wrong Option is Incorrect**
**Option A:** Without knowing the specific option, generally, an incorrect choice might not adequately assess the anatomy or might be invasive without providing sufficient diagnostic information.
**Option B:** Similarly, this might be an option that does not directly visualize the rectum and anus or their connection.
**Option C:** This could be an option that, while useful in some contexts, does not provide the necessary detail for diagnosing anorectal malformations.

**Clinical Pearl / High-Yield Fact**
In cases of suspected anorectal malformations, especially with no anal opening but a dimple, it's crucial to remember that **invertogram radiographs** or **ultrasound** can be helpful in assessing the distance of the rectal pouch from the skin, guiding surgical management.

**Correct Answer:** Not provided in the query.