## Core Concept
The Glomerular Filtration Rate (GFR) is influenced by the resistance in the afferent and efferent arterioles, which are crucial for regulating renal blood flow and glomerular pressure. Changes in the diameter of these arterioles can significantly affect the GFR.

## Why the Correct Answer is Right
Constriction of the efferent arteriole increases the resistance to blood flow leaving the glomerulus, which increases the glomerular capillary pressure. This increase in pressure enhances the filtration rate, as more fluid is pushed out of the glomerular capillaries into Bowman's space. On the other hand, dilation of the afferent arteriole decreases the resistance to blood flow entering the glomerulus, which also increases the glomerular capillary pressure and, consequently, the GFR. Both of these changes work to increase the GFR.

## Why Each Wrong Option is Incorrect
**Option A:** This option would suggest a decrease in GFR, which contradicts the effects of efferent arteriole constriction and afferent arteriole dilation.

**Option B:** This option might suggest no change or an opposing effect on GFR, which does not align with the physiological responses to efferent constriction and afferent dilation.

**Option D:** This option suggests an opposing effect compared to what is expected from the described changes in arteriole diameters.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the GFR is very sensitive to changes in the resistances of the afferent and efferent arterioles. For example, in conditions like glomerulonephritis, the constriction of the efferent arteriole can help maintain GFR despite glomerular damage. Understanding these regulatory mechanisms is crucial for interpreting renal function tests and managing kidney disease.

## Correct Answer: C.