Which of the following best defines how rems are used for flexible font sizing.
a. Compression is used to reduce or expand font size to match the user's screen.
b. The font size specified in the HTML document's top-level heading becomes the standard.
c. Font size is determined by the user's browser settings, which override the CSS-specified sizes.
d. A rem gives a maximum and minimum pixel size for headings and context fonts.

The correct option is option b.

Explanation:

rem stands for Root Em which indicates that the value of Em defined in the HTML level becomes the standard unit and thus all the alternatives are used that the new value of font is the multiple of the standard Em defined in the HTML part of the code. Thus the correct definition is the font size specified in the HTML top level heading which becomes the standard to be used further.

i belive the answer you are looking for is d: the nether