**Core Concept**
Glucose absorption in the intestine is a vital process for energy production and requires specific transport mechanisms. The small intestine is specialized to absorb glucose, a monosaccharide, against its concentration gradient, utilizing a specific transport system.

**Why the Correct Answer is Right**
Glucose absorption in the small intestine is facilitated by the sodium-glucose cotransporter 1 (SGLT1) in the enterocytes. This cotransporter uses the energy from the sodium gradient to transport glucose against its concentration gradient, allowing for efficient absorption of glucose from the intestinal lumen into the enterocytes. This process is essential for normal glucose homeostasis and energy production.

**Why Each Wrong Option is Incorrect**
**Option A:** Xylose is a monosaccharide that can be absorbed in the intestine, but it is not transported against its concentration gradient. Instead, xylose absorption is a passive process that occurs through facilitated diffusion via the xylose transporter.

**Option B:** Mannose is another monosaccharide that can be absorbed in the intestine, but like xylose, its absorption is not against its concentration gradient. Mannose is absorbed through a different facilitated diffusion process.

**Option D:** Ribose is a monosaccharide that is not typically absorbed in the intestine. While ribose can be absorbed in the liver, its absorption in the intestine is not a significant process.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the small intestine is specialized for glucose absorption, and this process is critical for maintaining normal glucose homeostasis and energy production. The sodium-glucose cotransporter 1 (SGLT1) is the key transport mechanism for glucose absorption in the small intestine.

**✓ Correct Answer: C. Glucose. Glucose is the only sugar normally absorbed in the intestine against a concentration gradient.**