Which statement about a dry line is correct?

• A. It marks a boundary where sea-level pressure is highest.
• B. It separates hot, moist air from cooler, drier air.
• C. It marks a boundary separating hot, dry air from moist, warm air.
• D. It occurs only over oceans.

Answer: (C)

A dry line is defined by a sharp boundary in moisture content between two air masses. To the west sits hot, dry air, and to the east sits moist, warm air. The key feature is this strong humidity contrast, which often shows up as a large dew point difference across the line. This moisture boundary is what helps lift and destabilize the atmosphere, making the dry line a common focus for thunderstorm development, especially in spring and early summer in the plains.

So the statement that captures the defining idea is that the dry line marks a boundary separating hot, dry air from moist, warm air. It’s not about sea-level pressure, and it’s not limited to oceans—dry lines form over continental land as well.