Question

stationary front
a front that is not moving
leading edge of colder air that is replacing warmer air.
warm front
leading edge of colder air that is replacing warmer air.
leading edge of warmer air that is replacing cooler air.
cold front
when a cold front catches up to a warm front
leading edge of colder air that is replacing warmer air.

Explanation:

To determine the correct option for each front:

• Stationary Front: Defined as a front that is not moving. So the correct option is "A front that is not moving".
• Warm Front: The leading edge of warmer air replacing cooler air. So the correct option is "Leading edge of warmer air that is replacing cooler air".
• Cold Front: The leading edge of colder air replacing warmer air. So the correct option is "Leading edge of colder air that is replacing warmer air". (Note: The "when a cold front catches up to a warm front" describes an occluded front, but among the cold front options, the leading edge of colder air replacing warmer air is correct for a cold front’s definition.)

Answer:

• Stationary Front: A front that is not moving
• Warm Front: Leading edge of warmer air that is replacing cooler air
• Cold Front: Leading edge of colder air that is replacing warmer air