Complete extinction occurs when

a. all individuals of a species are eliminated.

b. all species in a community merge.

c. all organisms within niche migrate.

d. all of these are correct.

The appropriate answer is A. Extinction occurs when all individuals of a species are eliminated. Some organisms today are on the verge of extinction as their populations are very low. These animals are characterized as critically endangered. They include the Asian elephant, dugong and the mountain gorilla. Extinction occurs when an animal is not able to cope with the rapid changes of the environment. Changes can include habitat loss and climate change.