Question

what happens in a cold front?
a. a cold air mass catches up to a moving warm air mass, sliding over it.
b. a warm air mass collides with a stationary cold air mass, and slides under it.
c. a warm air mass becomes a cold air mass as it moves.
d. a cold air mass comes in under a warm air mass.

Explanation:

A cold front occurs when a cold air mass, which is denser, moves and replaces a warm air mass. The cold air, being denser, slides under the less - dense warm air mass.

• Option A: Incorrect. Cold air mass slides under, not just "catches up" in a non - specific sliding over way.
• Option B: Incorrect. It is the cold air mass that is moving (not stationary) and slides under the warm air mass.
• Option C: Incorrect. A warm air mass does not "become" a cold air mass in a cold - front process.
• Option D: Correct. A cold air mass (denser) comes in under a warm air mass (less dense) as part of the cold - front formation.

Answer:

D. A cold air mass comes in under a warm air mass.