**Core Concept**
Glucose and sodium ion (Na+) absorption in the gastrointestinal (GI) tract is a critical process for maintaining proper electrolyte balance and glucose homeostasis. This process involves the coordinated action of specific transport mechanisms along the intestinal epithelium.

**Why the Correct Answer is Right**
Glucose and Na+ absorption in the GI tract primarily occurs through a secondary active transport mechanism, facilitated by the sodium-glucose cotransporter 1 (SGLT1). SGLT1 is a membrane-bound protein that uses the electrochemical gradient of Na+ to drive the co-transport of glucose into intestinal epithelial cells. This mechanism is essential for the efficient absorption of glucose and Na+ from the intestinal lumen.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the primary mechanism of glucose and Na+ absorption in the GI tract.
**Option B:** This option is incorrect because it refers to a different transport mechanism, primarily involved in the absorption of amino acids, rather than glucose and Na+.
**Option C:** This option is incorrect because it does not specify the correct transport mechanism, and the term "passive diffusion" is too general and does not accurately describe the complex process of glucose and Na+ absorption in the GI tract.
**Option D:** This option is incorrect because it refers to a different type of transport mechanism, primarily involved in the absorption of nutrients in the small intestine.

**Clinical Pearl / High-Yield Fact**
The sodium-glucose cotransporter 1 (SGLT1) is the primary mechanism for glucose and Na+ absorption in the GI tract, and its dysfunction can lead to glucose-galactose malabsorption, a rare genetic disorder characterized by the inability to absorb glucose and galactose from the intestinal lumen.

**Correct Answer:** C.