The correct answer is D) fast-moving cold front. Squall lines with an almost unbroken line of threatening dark clouds and sharp changes in wind direction typically precede the passage of a fast-moving cold front. As the cold front approaches, the changing wind direction and rapidly deteriorating weather conditions are hallmarks of this type of frontal system. In contrast, occluded fronts, slow-moving warm fronts, and stationary fronts do not exhibit the same dramatic changes in wind and cloud cover that are associated with fast-moving cold fronts.