The correct answer is C) relative intensity of different harmonics in each note.
The unique sound quality of a clarinet or a violin is caused by the relative intensity of different harmonics in each note.
Let's put the example of the violin. Its peculiar sound is the result of the combination of the diameter of the string, the point of contact of the bow, the pressure and speed of the bow, and the string you are playing. These produce the level of oscilation to produce the string's vibration. Nothing is predetermined. It is theviolinist who decides the timbre of the instrument.