Final answer:
To indent just the first line of a paragraph using the horizontal ruler, you can either drag the ruler to the desired position or double-click the ruler.
Step-by-step explanation:
To indent just the first line of a paragraph using the horizontal ruler:
- Drag the ruler to the desired position.
- Double-click the ruler.
Option A and B are both correct methods to achieve the desired indentation. Option C, right-clicking and selecting 'Indent', is not the correct way to use the ruler for indentation. Option D, pressing the Tab key, can create an indentation but it will affect the whole paragraph, not just the first line.