What has caused the widespread decline of the American chestnut tree? O global warming
O changes in farming habits
O a fungus
O scientist

Chestnut decline, attributed to blight, is caused by an Asian bark fungus (Cryphonectria parasitica), which was unknowingly imported from Asia on infected Chinese Chestnut trees. ... It particularly devastated trees in the Appalachian region, where up to 25% of the trees were American Chestnuts.

Explanation:

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c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.