A．the greenhouse gas effect produced by human activities tends to have a much greater environmental effect than that of volcanic explosions
B．clouds of sulfur-rich gases tend to achieve greater heights in the stratosphere than do ash clouds
C．a particular explosion producing high sulfur and little ash had a greater environmental effect than the converse
D．the burning of fossil fuels tends to exacerbate the effects of sulfurous aerosols, but not those of ash clouds
E．global warming effects tend to minimize the impact of ash clouds, but not those of sulfurous aerosols