What two types of maintenance are performed without distinction as to levels?

The correct answer highlights that rework and upkeep are types of maintenance that can be performed without distinct levels. Rework refers to the actions taken to restore an item or system to a desired operational condition, often involving significant alterations or repairs. Upkeep, on the other hand, encompasses the routine actions necessary to maintain an asset's function and appearance, usually through routine maintenance tasks.

Both rework and upkeep can be executed independently of predefined levels, as they can be applied on demand depending on the condition of the equipment or aircraft, rather than being bound to scheduled intervals or tiered assessments. This reflects the flexibility required in maintenance practices to ensure that systems remain operational and safe.

In contrast, choices like inspection and repair typically denote distinct actions often categorized by maintenance levels, while preventive and corrective maintenance are more aligned with structured procedures. Preparation and execution, though relevant in a general operational context, do not specifically pertain to the maintenance tasks being asked about. Therefore, rework and upkeep are appropriately categorized as types of maintenance that can be carried out independently of the defined levels.