Hey there! Hello!
Not sure if you still need this answer, but I'd love to help out if you do.
In terms if Excel Spreadsheet, your answer will be D. A moving dashed line border appears around the cells. What the copy button does is take the contents in your cell(s) and copies them so that you can paste them elsewhere. B and C would apply here if you were cutting the text, which clears whatever you have selected so that you can paste them elsewhere without having to go back and delete it.
I have attached an example of what happens to a cell when you either right click it and press copy, or press ctrl/command+c, which is the keyboard shortcut for copying text or contents.
Hope this helped you out! Feel free to ask me any additional questions if you have any. :-)
