Final answer:
Timbre is the characteristic of sound that makes it unique from others, even if they have the same pitch and volume, and is not concerning its wavelength or frequency. To determine which elements of sound change in a clip, listen for differences in pitch, volume, and the distinct quality of the sound being produced.
Step-by-step explanation:
Timbre is the quality of a sound that distinguishes it from other sounds of the same pitch and volume. Contrary to common misconception, timbre is not affected by the pitch or wavelength but rather by the complex interplay of sound wave frequencies, amplitudes, and the timing of the sound waves. Therefore, statements c and d, which suggest that timbre is the pitch or wavelength of sound, are incorrect. Instead, timbre relates to a sound's purity and is what makes different musical instruments playing the same note at the same loudness sound distinct from one another.
Regarding the elements of sound, wavelength/frequency/pitch correlate with how high or low a sound is perceived, amplitude/volume is related to the loudness of the sound, while timbre refers to the sound's color or quality. When identifying changes in a sound clip, one must listen for alterations in any of these elements to determine what aspect of sound is varying.