To quickly resize an object while maintaining its proportions, which key do you hold?

Holding down the Shift key while resizing an object in Adobe Illustrator allows you to maintain its original proportions. This is essential when you want to ensure that the height and width of the object scale uniformly, preventing distortion of the shape. For example, if you are resizing a circle and want to keep it a perfect circle instead of turning it into an oval, using the Shift key ensures that the ratio of width to height remains constant.

In contrast, other keys like Ctrl or Alt serve different functions; for instance, Ctrl typically allows for resizing an object from the center or duplicating it, while Alt enables you to create a copy of the object while scaling. The Spacebar is commonly used for moving the object rather than resizing it. Each key has its specific purpose, but the Shift key is specifically designed to help maintain proportions during resizing.