Final answer:
The infectious period of varicella, or chickenpox, lasts from about 2 days before the onset of the rash until all the lesions have scabbed over.
Step-by-step explanation:
The infectious period of varicella, or chickenpox, lasts from about 2 days before the onset of the rash until all the lesions have scabbed over. This means that the child with varicella is contagious during this entire period. The correct answer is option a) Lasts until the rash disappears.