I wrote a wonderful Subject-Verb Agreement chapter section https://www.academia.edu/2057551/Subject_Verb_Agreement_Module that has had nearly 2000 reads at Academia.edu. First, I sent it to Connexions of Rice University. Hailey MacArthur, a Composition Instructor and Linguistics researcher at Florida International University, found another rule amidst the 20 Most Common Grammar Errors by Bedford-St. Martin’s. http://bcs.bedfordstmartins.com/everyday_writer/20errors/14.html Go to #14 for Subject-Verb Agreement. You’ll find in their rule #6 when a relative pronoun (who, which, that) follows an interrupting phrase between the subject and verb, that verb may agree with the object of the preposition instead of the subject. Example from Bedford St. Martin’s: “Johnson was one of the athletes who were disqualified.” In a future edition of my 8 Rules of Subject-Verb Agreement, this will be Rule 2B. “Words between the Subject and Verb.” This link will be inserted at that Academia.edu site.