**Core Concept**
Chickenpox, caused by the varicella-zoster virus, is characterized by a distinctive rash that progresses from macules to papules, vesicles, and eventually crusts. The rash typically involves multiple stages of lesions at different stages of development.

**Why the Correct Answer is Right**
The rash of chickenpox is highly contagious and can spread from person to person through direct contact with the lesions or through airborne transmission. The lesions start as macules, which are flat, discolored areas, and then progress to papules, which are small, raised bumps. These papules eventually rupture to form vesicles, which are fluid-filled blisters. The vesicles then crust over and form scabs as they heal.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because chickenpox rash does not typically start with pustules, which are pus-filled bumps.
**Option B:** This option is incorrect because the rash of chickenpox does not usually start with petechiae, which are small, pinpoint spots caused by bleeding under the skin.
**Option C:** This option is incorrect because the rash of chickenpox does not typically start with bullae, which are large, fluid-filled blisters.

**Clinical Pearl / High-Yield Fact**
The rash of chickenpox can be contagious even before the rash appears, typically 1-2 days before the onset of the rash, and continues to be contagious until all the lesions have crusted over.

**Correct Answer: D. The rash of chickenpox progresses from macules to papules, vesicles, and eventually crusts.**