John

Which one of the following, if true, most strengthens the argument?

John of Worcester, an English monk, recorded the sighting, on December 8, 1128, of two unusually large sunspots. Five days later a brilliant aurora borealis (northern lights) was observed in southern Korea. Sunspot activity is tpyically followed by the appearance of an aurora borealis, after a span of time that averages five days. Thus, the Korean sighting helps to confirm John of Worcester's sighting.

Answer: Only heavy sunspot activity could have resulted in an aurora borealis viewable at a latitude as low as that of Korea.

This is a big time strengthener. It eliminates alternate causes - in fact, it eliminates all other alternate causes! This one is a home run for our argument in the stimulus.