a member of the marching band tunes their trombone inside their school. when they walk out to the field the instrument goes out of tune. what is the best explanation for this?

a) the instrument expands or contracts as temperature changes.
b) the speed of sound decreases with a decrease in temperature.
c) walking with the instrument loosens up joints on the instrument.
d) the air outside has a different humidity than the air inside changing the notes.