The answer is 3: Henry Ford adapted the assembly line, <em>an innovation in</em> <em>factory prodution</em>, to produce cars.
An appositive phrase is a noun phrase that <em>adds importantl information</em> or <em>adds descriptive words</em> that help make the sentence more detailed. But the <em>information can be removed without changing the grammar and meaning of the sentence</em>: "Henry Ford adapted the assembly line to produce cars." the appositive sentence is only <em>describing</em> what assembly line is.