B. varying the pitch of your voice
Anything verbal refers to your voice, talking or sound. The only option that has anything to do with sound/talking is varying the pitch of your voice. The other options are nonverbal strategies because they do not involve the sound your voice makes. Maintaining eye contact, using gestures and facial expressions are all nonverbal strategies. Using notes subtly is also a nonverbal strategy to help the speaker make eye contact rather than read the speech of a piece of paper or prompter.