Answer: Different vocal tract and harmonics
Step-by-step explanation:
We are given that a small boy and a grown woman both speak at approximately the same pitch.
To distinguish between the two, we check their harmonics which is different for both of them owing to the different vocal tracts they have. Owing to different vocal tracts, they each produce different harmonic which is actually the multiple of frequency of the wave. Thus, we can make the determination using this.