**Core Concept**
Colon cancer (Ca colon) is a malignant neoplasm of the large intestine, often requiring prompt diagnosis and treatment. The investigation of choice for colon cancer is a critical step in its management, involving a combination of imaging modalities and endoscopic techniques.

**Why the Correct Answer is Right**
The correct investigation of choice for colon cancer is colonoscopy, which allows for direct visualization of the colonic mucosa, biopsy of suspicious lesions, and polyp removal. Colonoscopy also enables the detection of synchronous cancers and the identification of high-risk lesions. The procedure involves the insertion of a flexible endoscope through the rectum, allowing for examination of the entire colon. The sensitivity and specificity of colonoscopy make it the gold standard for detecting colon cancer and its precursors.

**Why Each Wrong Option is Incorrect**
**Option A:** CT scans of the abdomen and pelvis are useful in staging colon cancer but are not the investigation of choice for initial diagnosis.

**Option B:** MRI colonography may be used as an alternative to colonoscopy in certain cases, but it is not the preferred method due to its lower sensitivity and specificity.

**Option C:** Barium enemas are an older technique that involves the use of X-rays to visualize the colon and are less commonly used today due to the availability of more sensitive and specific methods like colonoscopy.

**Clinical Pearl / High-Yield Fact**
Colonoscopy is the most effective method for preventing colon cancer through the removal of precancerous polyps, making it a critical tool in the management of this disease.

**Correct Answer:** C.