## Core Concept
The Glomerular Filtration Rate (GFR) is a critical indicator of kidney function, representing the rate at which fluid filtered by the glomeruli is passed into Bowman's capsule. It is influenced by various factors including changes in blood pressure, blood volume, and renal vascular resistance. Autoregulation is a key mechanism that maintains a relatively constant GFR over a wide range of blood pressures.

## Why the Correct Answer is Right
The correct answer, **C. Afferent arteriole dilation and efferent arteriole constriction**, is associated with an increase in the glomerular hydrostatic pressure, which increases GFR. Conversely, the opposite scenario - **afferent arteriole constriction and efferent arteriole dilation** - decreases the glomerular hydrostatic pressure, thereby decreasing GFR. However, among the provided options, we need to identify which one leads to a decrease in GFR.

## Why Each Wrong Option is Incorrect
- **Option A:** Afferent arteriole constriction and efferent arteriole dilation would actually increase the resistance to blood flow into the glomerulus while increasing the resistance to blood flow out of the glomerulus, respectively. This combination increases glomerular pressure and thus would increase GFR, not decrease it.
- **Option B:** Afferent arteriole dilation and efferent arteriole dilation would decrease the resistance to blood flow into and out of the glomerulus, respectively. This generally decreases glomerular hydrostatic pressure but the effect on GFR can vary; however, it's not the best option for decreasing GFR compared to the direct effect of constricting afferent arterioles and dilating efferent arterioles.
- **Option D:** Afferent arteriole dilation and efferent arteriole constriction increase GFR by increasing glomerular hydrostatic pressure.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that GFR is maintained within a narrow range despite fluctuations in blood pressure due to renal autoregulation. This autoregulation involves both afferent and efferent arteriolar responses to changes in blood pressure. For instance, in **renal artery stenosis**, the decreased pressure sensed by the juxtaglomerular apparatus leads to **afferent arteriole dilation** (to increase GFR) and **angiotensin II-mediated efferent arteriole constriction** (to further increase glomerular pressure). However, severe reduction in renal blood flow can overwhelm these compensatory mechanisms, leading to decreased GFR.

## Correct Answer: B.