Is it necessary to import the UnityEngine library and MonoBehaviour in every script?

In Unity, importing the UnityEngine library and the MonoBehaviour class is not always necessary for every script, particularly in cases where the script doesn't need to be attached to a GameObject. If a script is intended to be a utility or a static helper class, for instance, it may not require either of these imports.

The UnityEngine library provides access to Unity-specific classes and operations, and MonoBehaviour allows a script to inherit functionalities tied to GameObjects within a scene, such as event methods like Start and Update. If a script does not need to interact with these features, then it does not require the UnityEngine and MonoBehaviour imports, which can be the case for standalone classes that manage data or perform non-Unity related functions.

This context also clarifies the other choices; if a script is not applied to a GameObject, it won’t benefit from the MonoBehaviour’s event-driven model, which justifies the correctness of the selected response. In contrast, if your script is specifically working with UI or other Unity components, importing would be a requirement, but that situation does not apply universally to all scripts.