**Core Concept**
The assessment of tubal patency is crucial in diagnosing and treating infertility, ectopic pregnancy, and other conditions related to the fallopian tubes. Fallopian tube patency can be evaluated using various diagnostic tests, each with its own advantages and limitations.

**Why the Correct Answer is Right**
The correct answer is **hysterosalpingography (HSG)**, which is a radiological procedure that uses X-rays to visualize the fallopian tubes and uterus. HSG involves the injection of a contrast medium through the cervix, which highlights the tubal anatomy and detects any blockages or abnormalities. This procedure is particularly useful in assessing tubal patency, as it can identify both proximal and distal tubal occlusions.

**Why Each Wrong Option is Incorrect**
**Option A:** Laparoscopy is a surgical procedure that allows for direct visualization of the fallopian tubes, but it is more invasive than HSG and is typically used to diagnose and treat conditions that require surgical intervention.

**Option B:** Sonohysterography (SHG) is an ultrasound procedure that visualizes the uterus and endometrium, but it does not provide adequate visualization of the fallopian tubes.

**Option C:** Computed Tomography (CT) scan is a radiological imaging modality that can visualize the abdominal organs, but it is not typically used to assess tubal patency.

**Clinical Pearl / High-Yield Fact**
When performing HSG, it's essential to use a small amount of contrast medium to avoid causing an allergic reaction or tubal spasm, which can lead to inaccurate results.

**Correct Answer: C. Hysterosalpingography (HSG) is the best investigation to assess tubal patency.**