______ is not one of William Shakespeare's four greatest tragedies.

A．the lack of experienced researchers
B．lack of access to southern China
C．lack of relevant rock samples
D．lack of well-preserved fossils

A．Environmental changes must have caused the end-Permian mass extinction.
B．Massive volcanic eruptions might have caused the end Permian mass extinction.
C．The disappearance of dinosaurs was a consequence of the end-Permian mass extinction.
D．Marine animals appeared as a result of the end-Permian mass extinction.