OC619 is correct. The air cools at the Dry Adiabatic Lapse Rate until reaching the dew point. But the Dew point temp is a moving target.
sfc T = 25º
Dew Point = 22º
∴ T-D Spread (TDS) = 3º
Dew Point Lapse Rate = 0.5º/1000'
Dry Adiabatic Lapse Rate = 3º/1000'
DALR-Dewpoint Convergence (CR) = 2.5º/1000'
TDS ÷ CR = 3 ÷ 2.5 =
1.2 or 1200'
The 400'/deg C of temp-dewpoint spread mentioned in one of the posts is correct. The answer "C - 1000ft" is inaccurate but may be best of the choices.