Question: How does the rem unit represent a font size?

1. Font sizes are expressed relative to the font size of the containing div element
2. Font sizes are expressed relative to the font size of the parent elements
3. Font sizes are relative to the base font size of the operating system.
4. Font sizes are relative to the root em unit used in the HTML element.

Answer: The correct answer of the above question is Option D:Font sizes are relative to the root em unit used in the HTML element.