A police car is parked by the side of a highway and its siren emits a sound measuring 750 Hz. As you approach the police car from a distance, you hear a change in the sound. The change is in the sound's

A) frequency only.
B) pitch only.
C) frequency and wavelength.
D) pitch and frequency

It’s D) Pitch and frequency

Explanation: As you approach the police car with blaring siren, you hear a change in pitch and frequency. The apparent pitch changes as a result of the Doppler effect. Frequency determines pitch; frequency and wavelength are inversely proportional. You wouldn’t “hear“ either one. The result is pitch.

there is no correct list among the choices you've provided.

the list might look something like this:

-- baby human

-- piccolo

-- flute

-- soprano singer

-- trumpet

-- tenor singer

-- trombone

-- baritone singer

-- baritone horn

-- bass singer

-- tuba

since i had to make up the list myself, i made it easy on myself, and i didn't try to shuffle the string instruments and woodwinds into it too.