Hey there,
Your question states: What are some ways you can vary your tone of voice to help you communicate effectively with others?
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Your correct answer would be (Checking your inflection). The reason is so because as you checking your inflection, you would adjust your tone of voice, and make your speech with alot of inflection which would conclude in having the audience paying great attention to what you have to say with speaking.
Hope this helps.
~Jurgen