Which Statement Best Defines Mass Depletion

Which statement best defines mass depletion? 

A)  The normal extinction rate of various species as a result of changes in local environmental conditions. 
B)  A widespread, often global period during which extinction rates are higher than normal. 
C)  A catastrophic, widespread, often global event in which major groups of species are wiped out over a very short period of time. 
D)  The current extinction rate when the background extinction rate is subtracted from the mass extinction rate.