A developer must use print-314% in a webpage.

In HTL, theformatoption in the data-sly-use or data-sly-test attribute can be used to format values according to a pattern. The pattern'-#.##%'indicates that the number should be formatted as a percentage with up to two decimal places. ThepiValuevariable would be the number to format, and in this example, it would convert -3.14 to -314%. The@symbol is used to denote the use of an option with the variable in HTL.

Options B and C are incorrect because they do not use the correct syntax for the format option in HTL. The use of@is to specify options and not part of the variable or pattern itself.