Which criterion is true regarding feature classes stored within a feature dataset?

Feature classes stored within a feature dataset must have the same coordinate systems to ensure spatial consistency and integrity across the dataset. This requirement is critical because feature datasets are designed to group related feature classes that share a common spatial reference, thereby facilitating analysis and operations that involve multiple layers of information.

If the feature classes had differing coordinate systems, it could lead to difficulties in performing geospatial analysis or data visualization, as features from different coordinate systems would not align properly. This consistency allows for operations such as spatial joins, overlays, and geoprocessing tasks to be executed without the complications that arise from transforming data on-the-fly.

The option suggesting that feature classes can only be used within the file geodatabase is inaccurate, as feature classes can also be used in other geodatabase types and contexts. Although there's a statement about feature classes not being editable in ArcMap, this is not true as they can be edited depending on the user's permissions and the specific software capabilities. Lastly, the idea that feature classes can have differing coordinate systems directly contradicts the foundational requirements of a feature dataset. Thus, the requirement for uniformity in coordinate systems is essential for maintaining the integrity and functionality of the feature dataset.