From this passage we can infer that the author's attitude toward the theory of some geologists (Line 3, Para. 1) is _______.

A．it is nature itself that should take the blame for the decline of North Africa
B．climatic changes coupled with forest abuse result in the decrease of forests in North Africa
C．without sufficient forests, the rains will take away all the organic nitrogen
D．since Roman times the rain forests in North Africa has been decreasing gradually

A．can be classified into two types
B．is formed along the margins of the plates
C．consists of semi-molten rocks
D．is about 70 to 100 kilometers thick