Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: When a new air mass moves over a region it brings its characteristics to the region. This may change the area's temperature and humidity. Moving air masses cause the weather to change when they contact different conditions. For example, a warm air mass moving over cold ground may cause an inversion. Answer: warm air
Output:
An inversion may result when what kind of mass moves over cold ground?