The type of clause that the clause or the phrase does have is in letter C. adverbial clause. Adverbial clause is a dependent clause that functions as an adverb; that is , the entire clause modifies a verb, and adjective, or another adverb. I hope you are satisfied with my answer and feel free to ask for more
It should be "Mr. Blakely knew Seth made a bad decision. He told him so." since there's no period to differentiate between the transition, it is a run-on sentence.