In the winter of 1999, many central and northeastern states received less snow in winter than the average. Scientists have proposed several reasons for the situation. One possible factor is global warming; however, scientists still know very little about this phenomenon. Another credible reason for less snowfall is La Niña, which causes unusually cold ocean temperatures in the Equatorial Pacific. The result of a strong La Niña is greatly increased snowfall in the northwest and less snowfall in the central and northeastern United States. Thus, it may appear that there is less snow in a given year.

It may be inferred from the selection that

many environmental factors influence average annual snowfall.


At least two possible reasons—La Niña and global warming—are given as factors in decreased average annual snowfall. Thus, you must reason that there may be other factors that work together to influence average annual snowfall.

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