Answer:
A gain; lower
Explanation:
When an aircraft is flying in a region of warm air, the altitude is higher than the one the altimeter indicates. On the other hand, when the air is cold, the actual altitude is lower.
Given these facts, if the aircraft flies from warm to cold air, the altimeter will read too high, when in fact, the altitude will be lower. Conversely, if the aircraft flies from cold to warm air, the altimeter will read too low, when in fact, the altitude is higher.
