Some scientists claim that amphibians are currently experiencing a period of mass extinction. Which of the following should be included in an alternative hypothesis that would best support this claim? A. The current extinction rate of amphibians compared with the background rate of extinction as determined by the fossil record B. The extinction rate of amphibians in the 21st century compared with the extinction rate of amphibians during the 20th century C. The number of species of amphibians currently alive compared with the number of amphibian species known to be extinct D. The number of new amphibian species being discovered per year compared with the number of amphibian species becoming extinct during the same time period