The correct answer is C) 12 thrust shoes. The main engine thrust bearing typically contains 12 thrust shoes, which are the components responsible for supporting and distributing the thrust load generated by the engine. This configuration is a standard design for marine propulsion systems and is in accordance with the industry standards and practices for engine thrust bearing construction. The other answer choices are incorrect because 6 thrust shoes would be an unusually low number, 10 or 20 thrust shoes would be less common configurations, and 12 thrust shoes is the most prevalent and widely used design for this type of thrust bearing in marine applications.