**Core Concept**
The formation of renal calculi (kidney stones) is influenced by various factors, including metabolic disorders, dehydration, and changes in the composition of the urine. In this case, massive bowel resection leads to a significant alteration in the body's absorption of certain nutrients and ions.

**Why the Correct Answer is Right**
Massive bowel resection results in the malabsorption of bile salts, which in turn leads to an increased absorption of calcium in the colon. This increased calcium absorption, combined with the reduced absorption of oxalate, results in an increased concentration of calcium oxalate in the urine. This is a key factor in the formation of calcium oxalate renal calculi.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not directly related to the formation of renal calculi in massive bowel resection.
**Option B:** While dehydration can contribute to the formation of renal calculi, it is not the primary reason in this specific scenario.
**Option C:** This option is incorrect as the formation of renal calculi is not primarily due to the increased absorption of oxalate in the colon.

**Clinical Pearl / High-Yield Fact**
Remember the "Four F's" of kidney stone formation: **F**amily history, **F**luid status, **F**ood intake, and **F**actors that alter urine composition (such as bowel resection).

**Correct Answer: C. Increased absorption of oxalate**