To change the speed of an animation in CSS, which of the following properties should be adjusted?

To change the speed of an animation in CSS, the duration property is key. This property defines how long an animation takes to complete one cycle, essentially controlling the speed at which the animation progresses from start to finish. By adjusting the duration, you can make the animation play faster or slower, based on the value you set (in seconds or milliseconds).

For instance, setting a shorter duration value will result in the animation running quickly, while a longer value will slow it down. This property directly impacts the visual experience of the animation, allowing designers to tailor the timing according to their desired effect.

The other options relate to different aspects of animation. Speed isn't a dedicated CSS property for handling animation speeds; the timing-function is used to control the pacing of the animation between the start and end, and delay defines how long to wait before starting the animation. However, they do not directly change the overall duration or speed of the animation itself.