Which type of wood has been saturated with a preservative to enhance durability?

The correct answer is pressure treated wood, as this type of wood undergoes a special treatment process where preservatives are forced into the wood fibers under high pressure. This method significantly enhances the wood's durability, making it resistant to damage from moisture, insects, and decay. The preservatives used in this process help to extend the lifespan of the wood, making it a popular choice for outdoor applications such as decking, fencing, and other structures exposed to the elements.

In contrast, normal untreated wood does not have any protective treatment, making it more susceptible to environmental factors. Hardwood generally refers to a classification of timber from deciduous trees and does not imply any protective treatment. Plywood, while engineered for strength and stability, lacks the specialized preservatives that pressure treated wood contains, thus not offering the same level of durability against decay and pests.