Final answer:
In CAD programs, the 'Close the loop' option under the line command is used to automatically create a line segment that connects back to the starting point, thus closing the shape without the need to manually input the start coordinates again.
Step-by-step explanation:
When using the line command in many computer-aided design (CAD) programs, the option that allows us to quickly create a line segment connecting back to the starting point is A) Close the loop. This command option is typically used when you have drawn a series of connected lines and you want to close the shape with a final segment that returns to the start point, completing the loop without manually inputting the coordinates.
For instance, if you're drawing a polygon, you'd use the line command to create the sides of the shape. After the last side is drawn, instead of trying to match the endpoint with the initial point precisely, you can simply use the 'Close the loop' option, which automatically draws a line back to the starting point and closes the shape.