Seasonal variations in Earth's climate are caused by

The earth orbiting around the sun.

Explanation:

Before reading this explanation please bare in mind that the earth's axises are tilted and not in one straight line. Now as the earth orbits around the sun it is subjected to different angles each and everytime these different angles result in different amounts of sunlight striking the earth therefore the temepratures will differ changing the cimate and these changes are seasonal, we have four of them and they are known as our four seasons

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

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

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