Which explains what happens to a warm air mass at a warm front?
a.
a warm air mass overtakes a cold one, and the warm air rapidly rises and cools. the water in the air condenses to form clouds and severe thunderstorms.
b.
a warm air mass overtakes a cold one, and the warm air gradually rises and cools. the water in the air condenses to form clouds and severe thunderstorms.
c.
a warm air mass overtakes a cold one, and the warm air gradually rises and cools. the water in the air condenses to form clouds and moderate precipitation.
d.
a cold air mass overtakes a warm one, and the cold air gradually sinks and warms. the water in the air condenses to form clouds and moderate precipitation.