The correct answer is: A. the number of dots per inch.
In pen plotters, “resolution” refers to the shortest possible line. In electrostatic plotters, it refers to the number of dots per inch. The number of dots per inch is the number of dots that can be printed on a page in a single inch. The higher the number of dots per inch, the sharper the image will be.
Option B is incorrect because the speed per inch is not a measure of resolution. The speed per inch is the speed at which the plotter can move the pen across the page.
Option C is incorrect because dual-axis tracking is not a measure of resolution. Dual-axis tracking is a feature that allows the plotter to move the pen in two directions, up and down and left to right.
Option D is incorrect because how accurately the plotter returns to a specific point is not a measure of resolution. How accurately the plotter returns to a specific point is a measure of accuracy.
Option E is incorrect because the number of dots per inch is a measure of resolution in electrostatic plotters.