What command is used to add length to lines in a sketch?

The command used to add length to lines in a sketch is the Extend command. This command allows users to extend the endpoints of a line or arc to meet with another entity, effectively increasing their length to reach another object or guideline within the sketch. The Extend command is particularly useful for ensuring that lines connect precisely, creating a more refined and accurate sketch without the need to manually adjust the lengths of multiple lines.

In contrast, the Fillet command is typically used to round the corners where two lines meet, rather than extending their lengths. Drive Joint is a command used to define rotational or linear motion for assembly constraints, and Extrusion refers to a process of creating 3D shapes from 2D sketches by extending them into the third dimension, which does not pertain to altering the length of lines within a sketch. Thus, the Extend command is specifically designed for modifying the length of lines, making it the correct choice.