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13. succession is possible because
a. existing plants reproduce quickly.
b. new species make the environment less suitable for previous ones.
c. climates change over time.
d. it is a rapid and chaotic process that is very difficult to control.

The correct option is b. new species make the environment less suitable for previous ones.

Explanation:

In ecology, succession can be described as the changes in a species structure over a period of time. In a community, newer species tend to have better characteristics and adaptations to survive in a community as compared to the older ones. As a result, the new species begin to take over the land and the older ones gets removed. It is due to ecological succession that climax communities are formed from pioneer species.

I think it might be C or D