Final answer:
Use the command pendown() or pd() to allow the turtle to draw a line during movement in turtle graphics.
Step-by-step explanation:
To enable the turtle to draw a line during movement in the turtle graphics library, you would use the command pendown() or its shorthand version pd(). This command tells the turtle to touch the pen to the canvas, thereby drawing a line as it moves. To start drawing, you would first initiate the turtle, then call pendown(), and proceed with movement commands like forward() or fd() for the turtle to move and draw a line.