Fact 1: Temperature falls from lower to higher altitudes. Fact 2: Temperature values are in degrees celsius. Given the two facts above, what falls from lower to higher altitudes?

Pick from:
a). gravity;
b). colder and wetter;
c). water vapor;
d). kinetic energy;
e). density;
f). degrees Celsius;
g). heat energy;
h). altitude;
The answer is:
f).