Scientists have noted a decline in the number of mushroom species dating back to the early 1900s. Annual crops of edible mushrooms in France and Germany have declined since 1950. One hypothesis explaining the decline is that edible fungi are being overharvested. Global warming and air pollution have also been considered as part of the problem. Researchers have also determined that the amount of edible fungi harvested tripled from 1900 to 1950.

This last piece of evidence bolsters which hypothesis?

A) Overharvesting may be the reason for the decline in fungi.

B) Global warming is the primary cause of the decline in fungi.

C) Air pollution is the factor which causes the largest decline in fungi.

D) Overharvesting, in combination with global warming, has caused the decline in fungi.