Meteorologists Can Distinguish a Cold from a Warm Front Because

Meteorologists can distinguish a cold from a warm front because a cold front occurs when a cold air mass __________ , whereas a warm front exists where a ___________ .

A) advances under a warm air mass and forces the warm air to rise; cold air mass retreats and a warm air mass advances
B) retreats and a warm air mass advances; cold air mass advances under a warm air mass, which forces the warm air to rise
C) forces warm air to sink; warm air mass retreats and a cold air mass advances
D) Meteorologists cannot distinguish between the two air masses.