How much higher is the current global extinction rate than the usual background rate?
a. The current global extinction rate is 100 times higher than the usual background rate.
b. The current global extinction rate is 1,000 times higher than the usual background rate.
c. The current global extinction rate is 10,000 times higher than the usual background rate.
d. The current global extinction rate is 100,000 times higher than the usual background rate.
