Robert : What do you think about the global warming?
Tom : lthink we, all cause it with our activities.
Robert : What do you mean by that?
Tom : We cut trees, destroy forests. Also we pollute the sea, nature and air, so the glaciers melt and the sea level increases.
Which one is NOT a cause of global warming according to the dialogue above?
A) 
B) 
C) 
D) 