Out of the four options presented in this problem, the most probable answer would be A. humidity.
Weather has many characteristics which includes, but are not limited, to air temperature, wind speed, the directions of the wind, cloud cover, the type of clouds present, amount of precipitation, the type of precipitation, and of course humidity. Although B. winds is an option, it isn't ultimately a main characteristic since some weathers doesn't involve winds too much. The humidity, however, is present in all kinds of weather. The other characteristics help in differentiating which weather to which weather.