Answer
B - Passenger pigeons were driven extinct primarily by overharvesting.
Work Step by Step
Passenger pigeons were hunted to the point of extinction because they were removed from the environment faster than they were able to reproduce. It once was one of the most abundant species of birds in North America and traveled in continuous high density flocks, sometimes blocking out most of the sun. The high density flocks made it easier for hunters to shoot or net the birds in large numbers, and thus were over harvested.
