Classifying animals as endangered or threatened: a. occurs when there are fewer than 500 individuals within a population. b. makes legal tools available to protect the species. c. describes the likelihood of a species' continued survival. d. both b) and c) are correct. e. all of the above are correct.

a. occurs when there are fewer than 500 individuals within a population

Explanation:

An endangered species was a species that is the danger of the extinction an only significant part of this process remain and those species are at the likelihood of the extinction in the near future. As per the IUCN, the endangered species are those that have one that meets the criteria of about the 50 to 70% population which gets decreases over 10 years and has a  total area that has than 5,000 km that is a population of the area less than 500 km.

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