Both B and D use "publish" instead of published which is not on the correct tense, so we can rule those out. Then, I looked for another error, and you need an a before "patent clerk." So A, the other viable answer, was ruled out. C is correct.
This "italicized" part of the sentence is an adjectival dependent clause. It acts as an adjective to the word motorist and cannot stand alone without putting it with an independent sentence, such as "The motorist lost his way."