When did the last mass extinction occur?
o
a. at the beginning of this era.
o
b. at the beginning of this period.
o
c. at the beginning of this epoch.
o
d. at the beginning of this eon.

D. At the beginning of this era.

Explanation:

Just took the test.

At the beginning of this era

Explanation:

just got it right on APEX

true                                                                                                       true true true true true true

geologic time scale (for gradpoint) =)