What does intonation refer to select one of the options below as your a. the change in the pitch (high or low sound of the voiceb. the rate of speed at which a poem is readc. the flow of apoem's stressed or unstressed syllablesd. the emphasis of words through a change of pace?

I associate "Tone" with sound frequencies. Tonic solfa being a music example which is basically, I think, using a certain musical key signature such as C major. In a major scale the sequence of "musical intervals" (ie frequency steps) is  key note TONE TONE SEMITONE ... TONE TONE SEMITONE.octave higher than keynote.
So, I'd go for a here.