The correct answer is C) Piston pin bushing. A piston pin bushing is an example of a solid bearing, which is a type of bearing that uses a solid material, such as a metal or polymer, to support the load and reduce friction between moving parts. Piston pin bushings are used in internal combustion engines to support the piston pin, which connects the piston to the connecting rod, and they must be made of a durable, solid material to withstand the high loads and stresses. The other options are not examples of solid bearings. Turbo-generator turbine bearings and thrust bearings are typically fluid-film bearings, which use a thin layer of fluid, such as oil, to separate the moving surfaces and reduce friction. Spring bearings use a spring element to support the load, rather than a solid material.