A．presenting two competing scientific theories concerning solar activity and evaluating geological evidence often cited to support them
B．giving a brief overview of some recent scientific developments in solar physics and assessing their impact on future climatological research
C．discussing the difficulties involved in linking terrestrial phenomena with solar activity and indicating how resolving that issue could have an impact on our understanding of solar physics
D．pointing out the futility of a certain line of scientific inquiry into the terrestrial effects of solar activity and recommending its abandonment in favor of purely physics-oriented research