This is needed to introduce change into an animation:Group of answer choicesStageKeyframeTimelineFrame

To introduce change into an animation, the correct answer from the provided choices is "Keyframe."

Explanation

1. Keyframe: In animation, a keyframe marks a significant point in the timeline where changes in the properties of an object are defined. By setting keyframes at different points in time, animators can define the start and end points of an animated motion, enabling smooth transitions between these points.

2. Stage: This refers to the area where the animated content is displayed, but it does not directly influence how changes in the animation are implemented.

3. Timeline: The timeline is the overall framework where keyframes and events are arranged over time, but it is the keyframes that specifically denote changes within that timeline.

4. Frame: A frame refers to a single image in a sequence of images that compose an animation, but it doesn't imply a change itself.

In summary, keyframes are essential for introducing and defining changes in animations.