What materials form the bases of the three types of hydraulic fluids?

The correct response highlights that the three primary types of hydraulic fluids are based on vegetable, mineral, and phosphate esters. These categories of fluids are essential in hydraulic systems, particularly in aviation and other high-performance applications.

Vegetable-based hydraulic fluids are derived from natural plant sources and are known for their biodegradability and lower toxicity compared to petroleum-based fluids. Mineral-based hydraulic fluids are derived from refined crude oil and are widely utilized due to their availability and cost-effectiveness, providing good lubrication properties and stability under various operational conditions. Phosphate esters are synthetic fluids that offer high fire resistance and are particularly valuable in high-temperature and high-pressure environments.

The other options do not accurately represent the recognized categories of hydraulic fluids. For instance, the inclusion of saline in one option doesn't align with the primary fluid types used in hydraulic systems. Similarly, water is not a base material for hydraulic fluids, as it is typically not used due to its incompatibility with the requirements of hydraulic systems and potential to cause rust and corrosion. Therefore, the answer showcasing vegetable, mineral, and phosphate esters comprehensively encapsulates the basis of the three primary hydraulic fluid types used in aviation.