**Core Concept**
Minimal change disease (MCD) is a type of glomerulonephritis characterized by the loss of foot processes of podocytes on electron microscopy, but normal appearance on light microscopy. The glomeruli appear normal under light microscopy due to the preserved capillary walls and mesangial matrix.

**Why the Correct Answer is Right**
The normal appearance on light microscopy in MCD is due to the fact that the changes are primarily confined to the podocytes, which are not visible under light microscopy. The loss of foot processes in MCD is a result of the disruption of the slit diaphragm, a critical structure for maintaining the glomerular filtration barrier.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it implies that the glomeruli appear abnormal on light microscopy, which is not characteristic of MCD.
**Option B:** This option is incorrect as it suggests that the changes in MCD are visible under light microscopy, which is not the case.
**Option C:** This option is incorrect as it implies that the changes in MCD are confined to the mesangial matrix, which is not accurate.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the diagnosis of MCD is often made by demonstrating the loss of foot processes on electron microscopy, rather than the normal appearance on light microscopy.

**Correct Answer: C. Normal appearance on light microscopy.**