Assertion: Snow does not melt easily at mountains.
Reason: A decrease in pressure leads to an increase in freezing point.
A. `S` is correct but `E` is wrong.
B. `S` is wrong but `E` is correct.
C. Both `S` and `E` are correct and `E` is correct explanation of `S`.
D. Both `S` and `E` are correct but `E` is not correct explanation of `S`.