SkillsUSA Photography Practice Exam

Holding the Shift key while you draw constrains the line to a straight horizontal (or vertical) orientation. This constraint, often called snapping or a "constrain" feature, makes the line stay level as you move the cursor, ensuring a precise horizontal result. When you release the mouse, the line remains perfectly horizontal because the angle was locked during the drag.

The other keys don’t perform this exact function: the Spacebar usually pans the canvas, Alt often alters tool behavior or creates alternate actions, and Ctrl is used for various shortcuts like copying or selecting options. So the Shift key is the one that guarantees a perfectly horizontal line.