What is the correct representation for US currency format?

The correct representation for US currency format is indeed '$9,999.99'. This format aligns with standard conventions for denoting currency in the United States.

In this format, the dollar sign precedes the amount, which includes a comma separating thousands from hundreds, making it easier to read larger amounts at a glance. The period is used to indicate the decimal point, separating dollars from cents. Therefore, this representation accurately and clearly conveys the value of the currency, adhering to both accounting norms and common practice.

The other formats do not meet the standard for US currency. For instance, placing the dollar sign without commas or incorrectly using periods and commas as seen in the other options makes them less clear and could lead to misinterpretation of the amount being represented.