**Core Concept:** Sympathetic stimulation affects the glomerular filtration rate (GFR) through the renin-angiotensin-aldosterone system (RAAS) and the renal sympathetic nervous system (RSNS).

**Why the Correct Answer is Right:** When the sympathetic nervous system is activated, it leads to increased renal sympathetic nerve activity (RSNA), which in turn enhances the release of renin from the juxtaglomerular cells in the afferent and efferent arterioles of the glomerulus. This increased renin activity results in the activation of the RAAS, leading to the production and release of angiotensin II. Angiotensin II then constricts the afferent arteriole, which increases the filtration pressure in the glomerulus and thereby increases GFR.

**Why Each Wrong Option is Incorrect:**

A. **Incorrect Option A:** Angiotensin II is responsible for vasoconstriction, not vasodilation. This option is incorrect because it opposes the correct answer, which is that sympathetic stimulation increases GFR through the release of angiotensin II and its vasoconstrictive effect on afferent arterioles.

B. **Incorrect Option B:** Renin is a precursor to angiotensinogen, which is then converted to angiotensin II by the renin-angiotensin-aldosterone system (RAAS). This option is incorrect because it describes the pathway leading to angiotensin II production but does not explain the direct effect of sympathetic stimulation on GFR.

C. **Incorrect Option C:** Renal sympathetic nerve activity (RSNA) indirectly affects GFR through the RAAS. While RSNA influences the RAAS, the correct answer is that RSNA increases GFR directly through the constriction of afferent arterioles.

D. **Incorrect Option D:** Aldosterone is a hormone involved in sodium and potassium homeostasis, not directly affecting GFR. This option is incorrect because it discusses aldosterone, which is unrelated to the direct effect of sympathetic stimulation on GFR.

**Core Concept:** The renin-angiotensin-aldosterone system (RAAS) modulates blood pressure, electrolyte balance, and fluid volume in the body.

**Why Each Wrong Option is Incorrect:**

A. **Incorrect Option A:** RAAS is involved in blood pressure regulation and sodium reabsorption, but it does not directly affect GFR. This option is incorrect because it focuses on RAAS' role in blood pressure regulation rather than explaining the direct effect of sympathetic stimulation on GFR.

B. **Incorrect Option B:** Aldosterone is a hormone involved in sodium reabsorption and potassium homeostasis, not directly affecting GFR. This option is incorrect because it mentions aldosterone, which is unrelated to the direct effect of sympathetic stimulation on GFR.

**Correct Answer Explanation:**

The correct answer (C) emphasizes the role of renal sympathetic nerve activity (RSNA) in increasing GFR through the constriction of afferent arterioles. When RSNA is activated, it leads to the release of renin from the juxtaglomerular cells,