Everybody acts not only under external compulsion ______ (也要遵照内心的需求).

A．The climate of earth has fluctuated quite a hit over the last 4.6 billion years.
B．An increase in the earth’s temperature will have major consequences for all life on this planet.
C．The information we have got makes us unable to explain the global warming completely.
D．The Pleistocene began about 1.8 million years ago.