A．The conversion of volcanic waste to fertilizer.
B．The menace of currently dormant volcanoes around Mount Saint Helens.
C．The eruption of Mount Saint Helens and its effects on the environment.
D．The elimination of volcanic ash by natural means.

A．The distance-learning course is free of charge.
B．The distance-learning course is taught by professors overseas.
C．There is no regular class in the distance-learning course.
D．There is no exam in the distance-learning course.