The insolation changes over the course of the diurnal cycle are caused by (blank)

The insolation changes over the course of the diurnal cycle are caused by the daily rotation of the Earth.
The daily rotation of the Earth causes the progression of daytime and nighttime (which depends on which part of the Earth is facing the Sun), and the amount of solar insolation (which represents the amount of solar light falling on a given area). The fluctuations of the insolation result in both air and surface temperatures.

81 is a composite number

980 is the correct answer