In your own words, explain how changes in solar activity affected global climate in the past.

Explanation:

The climate is something dynamic, changing, even unrepeatable, a consequence of the energy that the Earth receives from the Sun and the exchanges of energy between different parts of what is called the Climate System, which we can understand as synonymous with planet Earth. Those parts or subsystems are:

The atmosphere, gas envelope of the planet, where we perceive the weather.

The hydrosphere, formed by oceans, seas, lakes, etc.

The lithosphere, solid crust emerging from the continents, where we live.

The biosphere, formed by all living beings, including man.

The cryosphere, formed by the ice that covers part of oceans and continents.

From a broad point of view, climate is defined as the state of the Climate System, including its statistical properties. It is precisely this that relates this definition of climate to the most classic, and restricted, consisting of considering it as a statistical description of environmental variables (for example, temperature, wind, surface humidity or precipitation) using average values and dispersion measures in long time intervals, much higher than typical atmospheric weather.

The indicated subsystems of the Climate System have very different dynamics. While some undergo appreciable continuous changes (the atmosphere, for example, with its succession of times - sunny, cloudy, windy, rainy, etc. - so different) others do so very slowly; so slowly, in some cases, that, for the life of man or several human generations, it makes no sense to consider its variability (as would be the case with the lithosphere, except for the more superficial soil layer). When the energy we receive from the Sun reaches the Earth, it is distributed among all the subsystems and exchanged between them, each of them attending to its own dynamics. From the difference between these exchanges arises the great variety of climates of the different regions of our planet, which we know so well and that are the manifestation of the spatial variability of the climate.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."