**Core Concept**
GIP is an incretin hormone secreted by the intestinal K cells in response to nutrient intake, particularly glucose and fat. It plays a crucial role in glucose metabolism by enhancing insulin secretion from the pancreas.

**Why the Correct Answer is Right**
GIP exerts its effects by binding to the GIP receptor on pancreatic beta cells, which activates the adenylate cyclase pathway, leading to increased intracellular cyclic AMP (cAMP) levels. This activation stimulates the closure of potassium channels, depolarization of the cell membrane, and ultimately, the opening of calcium channels, allowing calcium ions to enter the cell. The increase in intracellular calcium triggers the secretion of insulin.

**Why Each Wrong Option is Incorrect**
**Option A:** This option may be true, but without further information, it's unclear. If it's a statement about GIP, it may be correct, but we can't evaluate it without more context.
**Option B:** This option may be true, but without further information, it's unclear. If it's a statement about GIP, it may be correct, but we can't evaluate it without more context.
**Option C:** This option is incorrect because GIP is, in fact, glucose-dependent. Its insulinotropic effects are only observed in the presence of elevated blood glucose levels.
**Option D:** This option is incorrect because GIP's effects are primarily mediated through the GIP receptor on pancreatic beta cells, not through the GLP-1 receptor.

**Clinical Pearl / High-Yield Fact**
GIP's glucose-dependent insulinotropic effects make it an attractive target for the development of new therapeutic agents for the treatment of type 2 diabetes.

**Correct Answer: C. GIP is glucose-dependent.**