To know climate, the average of what is observed?

Correct answer: Weather over a long time

The governing concept is the distinction between weather and climate. Weather means the atmospheric condition at a particular place and time, such as today’s temperature, cloud cover, wind or rainfall. Climate is understood from the usual or average pattern of weather observed over a long period, generally several decades. Thus option C is correct because climate uses long-term weather observations rather than a single event or a single physical feature. A population figure does not define climate, and soil and river flow may be influenced by climate but are not its basic definition. One unusually hot day or one heavy shower cannot by itself establish the climate of a region; repeated observations over a long time are needed to identify its typical conditions.