Which phrase became synonymous with the research stanley milgram conducted on "the small world phenomenon"?

Which sentence corrects the error in pronoun-antecedent agreement? new team members should pick up his or her jersey from the activities office. if a team member is unable to attend a practice, he or she must provide a doctor's note. if students wish to compete, he or she must maintain a grade point average above 2.5. students are not permitted to attend away games without the consent of her parents or guardians.