According to the question, you have to remove all subtotals from the worksheet with the least administrative effort. You can remove all subtotals from a worksheet at a time. For this, take the following steps: Open the Subtotal dialog box by clicking the Subtotal option in the Outline group on the Data tab.
Click the Remove All option.

Answer option A is incorrect. No such option is provided in Excel 2010.

Answer option B is incorrect. Although this will hide the rows containing the subtotals, the contents will remain there and can be made visible by using the Unhide row option. Moreover, the question specifically specifies to remove all subtotals from the sheet.
Answer option D is incorrect. Although this step will accomplish the task, it will involve a lot of administrative burden of selecting each row and deleting it manually.
C