By which indicators do meteorologists identify the advance of the monsoon?

Correct answer: By changes in continuous rainfall, wind direction, clouds and humidity

Meteorologists identify the advance of the monsoon through a pattern of several connected weather changes. These include sustained or recurring rainfall, a change in wind direction, increasing cloud cover and rising humidity. A single shower may result from a local storm and does not by itself prove that the monsoon has arrived. Option A is correct because it includes multiple signs that together show the seasonal circulation is becoming established. The Moon, river length and mountain age are not operational indicators of monsoon onset.

The important idea is persistence and combination. When moisture-bearing winds reach a region, humidity often rises, clouds become more frequent and rainfall continues or returns in a characteristic pattern. Meteorologists examine observations over time and across areas rather than relying on one isolated event. Wind direction is especially useful because the monsoon involves a seasonal change in circulation. Thus option A gives a scientifically meaningful set of indicators, while the other choices have no direct basis for identifying monsoon advance.