Final answer:
Adiabatic cooling happens when an a. air mass rises and expands, leading to a decrease in temperature because no heat is exchanged with the surroundings and internal energy decreases.
Step-by-step explanation:
Adiabatic cooling occurs when an air mass rises and expands. This is because in an adiabatic process no heat is transferred into or out of the system.
When a gas or air mass expands adiabatically, it must do work against the surroundings causing its internal energy to decrease, which is reflected as a decrease in temperature. Therefore, the correct answer to the question is 'A. air mass rises and expands.'