In general, the highest relative humidity is observed and the lowest relative humidity is observed

In general, the highest relative humidity is observed NEAR SUNRISE and the lowest relative humidity is observed during MID-AFTERNOON.

Relative humidity is inversely proportional to temperature. The colder the climate, the higher the relative humidity. The hotter the temperatures outside, the lower the relative humidity.

Relative humidity increases as the air temperature falls at night and peaks at dawn.  

Temperature peaks during mid-afternoon, thus relative humidity is at its lowest.

i i think it might b c

81 is a composite number.