The best explanation is the <em>difference</em> between the inside <em>temperature</em> and the outside temperature.
If the player doesn't change his emboucher (muscles and position of his lips), then the pitch produced by the instrument depends only on the physical dimensions of its plumbing, and the speed of sound in the tube.
BOTH of those things change slightly when the temperature changes.
The answer for this question is negative externality
D is the amount of space object takes up