Answer:
Idea.
Explanation:
Patent can be defined as the exclusive or sole right granted to an inventor by a sovereign authority such as a government, which enables him or her to manufacture, use, or sell an invention for a specific period of time.
Generally, patents are used on ideas and innovation for products that are manufactured through the application of various technologies.
In this scenario, an auto mechanic has an idea to make a tool that will make his job easier. He has a machinist friend make a prototype of it.
Hence, a patent will protect the idea because it is an intellectual property of the auto mechanic.
