Yes, the overall pitch of your voice can be changed through practice or working with a speech therapist. It takes work, but it definitely can be done.
Voice pitch in a note sung by an individual:
if I were to sing an A flat, that would be my pitch. Seeing as all melodies are not comprised of only A flats, I would argue that voice pitch could, in fact, change quite drastically, as Christina Aguilera insists upon demonstrating at every available opportunity.
you can immediately answer questions your audience might have.
I'm not sure what you mean by this, but since you are asking under the category of public speaking I'm assuming you're referring to ethos, logos, and pathos.
Ethos refers to credibility. - How a speaker presents him/herself and is perceived by the audience falls under ethos. If a speaker is dressed nicely, speaks proper English, and uses appropriate nonverbal elements, the speaker may appeal to ethos very well. In some cases, ethos alone may make a speaker seem smart, regardless of how well the speaker uses logos.
Logos refers to logic. - Ethics aside, any information presented as fact by a speaker falls under logos.
Pathos refers to emotion. - Those sad dog commercials that play really depressing music and shows images of abused animals rely on pathos. If the audience feels sad/bad for the animals after watching one of those commercials, then the commercial appealed to pathos well.
Yes. This is just a normal progression of evolution. When a species reaches a standstill as the human race is experiencing, this is the normal thing to do. Enhanced sensory capabilities, if properly used, can be used in many progressive ways.
Rhythm, emphasis, volume, repetition, tone, are some.
You would normally go into the 'transition': a signal to the audience that you are starting the main body of your speech.