Scientists want to determine whether the rapid economic growth in China between 1950 and 2000 caused a mass extinction of animal species during that time period. A mass extinction event is considered to occur when the rate of species extinction for exceeds the background extinction rate. The scientists collected data on the number of extinctions of selected vertebrate species in China between 1950 and 2000, as shown in below Table . Extinction rates were ascertained by measuring the werage percent of species lost(PSL). The average percent of extinctions of 252 protected vertebrate specles in 2,365 countles in China from 1950 to 2000.

Mammals Birds Amphibians and Reptiles Background Rate
Average PSL ± 1 standard deviation 47.4 ± 339 19.75 ± 17.70 28.80 ± 28.86 27.21 ± 16.26

Which of the following is the null hypothesis most relevant for evaluating the data in Table?

a. There is no significant difference between the extinction rate of animals between 1950 and 2000 in China and the background extinction rate.
b. There is no significant difference between the extinction rates of mammals, birds, amphibians, and reptiles in China.
c. There is a significant difference between the extinction rate for mammals in China and the background extinction rate for mammals.
d. Because of climate change, habitat loss, pollution, and excessive exploitation of resources, China experienced a mass extinction event between 1950 and 2000.