A．It shows the structure of the earth.
B．It leads to new changes.
C．It may not be true.
D．It is an important revolution in scientific thought.

A．Places at the heart of continents.
B．Places where continents meet.
C．Places where the rock is not stable.
D．Places near the coastlines.

A．They emphasize the importance of presentations.
B．They provide the author's own presentation experience for us.
C． They tell the difference between good and bad presentations.
D．They teach people how to develop presentation skills.