Final answer:
To modify the outline weight of a text box to 3 pt, the correct action is to adjust the outline weight to 3 pt in the format options, not to change the font size, text color, or apply bold formatting.
Step-by-step explanation:
The question refers to modifying the weight of the outline of a selected text box. The action that should be taken to change the outline weight to 3 pt is C) Adjust outline weight to 3 pt. To achieve this, you should select the text box and then look for the outline or border settings in your software's format options, where you will find an option to change the weight (or thickness) of the outline. There you can set the outline weight to 3 pt. This does not involve changing the font size, text color, or applying bold formatting to the text itself; those actions affect the text's appearance, not the outline of the box in which the text is contained.