Psychrometrics: identify the variable that decreases during sensible cooling of air. Process: cool moist air with no dehumidification (humidity ratio essentially constant and above dew point). Select the property that definitely decreases in this process.

Given
Sensible cooling (no moisture removal) ⇒ humidity ratio (specific humidity) remains ~constant, dry-bulb falls.

Property trends
Dry-bulb temperature: decreases (by definition of sensible cooling).
Specific humidity: ~constant (no moisture added/removed).
Relative humidity: increases as air is cooled at fixed moisture content.
Wet-bulb temperature: typically decreases as enthalpy falls, but the most fundamental and unambiguous decrease is dry-bulb temperature.

Final Answer
dry bulb temperature.