Determine which of the following must change when pitch gets higher a.amplitude b.frequency c.wavelength d.intensity e.speed of sound waves

Higher pitch means higher frequency.

But higher frequency also means shorter wavelength, because the product of (frequency) x (wavelength) is the wave-speed, so it doesn't change.

So (b) and (c) must both change.

When the medium through which a wave travels suddenly changes, the wave often experiences partial transmission and partial refection at the interface. ... Transmission permits the passage of wave, with some or none of the incident wave being absorbed. Reflection and transmission often occur at the same time.