What is the shortcut for adding a first keyframe?

The shortcut for adding a first keyframe is often associated with specific layers' properties, depending on the context in which you're working. The correct choice for adding the first keyframe is the combination that uses the Alt key along with Shift and a letter corresponding to the property you want to animate. This combination provides a quick and efficient way to start keyframing, allowing users to add a keyframe to an adjustable property without navigating through menus.

By using the correct combination of the Alt and Shift keys with a specific property, users streamline their workflow in Adobe After Effects, enabling the rapid setup of animations. This is particularly valuable in a fast-paced working environment where efficiency is key to meeting deadlines or maintaining creative flow.

In contrast, other options mentioned don't directly correlate with creating keyframes. For instance, Ctrl + K opens the Composition Settings, Shift + K does not have a standard function for adding keyframes, and F9 is the shortcut used to easy ease keyframes after they've been created rather than adding the initial point of animation. Understanding these shortcuts and their specific applications can significantly enhance user productivity within After Effects.