Abandon railroad tracks are overgrown with weeds 10 years later there are small aspen trees growing in the middle of the tracks this change is an example

The correct answer is known as "Ecological Succession".

Ecological Succession refers to the  procedure of changes inside the species shape of an ecological community over the years. The time scale may be considered within many years or maybe a hundred of thousands of years after a mass extinction. There are two known classifications of Ecological Succession, known as Primary and Secondary.

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The correct answer is c.