The Greater Prairie Chicken of Illinois was once one of the most prevalent birds in the Great Plains and across North America. With habitat destruction and overhunting, a decline in the bird population occurred. The graph shows the number of male birds from the 1970s through the 1990s. An arrow indicates the year 1993, after which the population began to rebound.
What explanation best describes the data from the graph?

A) Prior to 1993, there was no habitat for the birds. In 1993, agricultural land was converted into bird sanctuaries, allowing birds to increase in number.
B) Prior to 1993, male Prairie Chickens were aggressive and killed each other to determine who would mate. After 1993, farmers domesticated the birds and controlled which males would mate to increase the population.
C) Prior to 1993, chemical pollution in the air and water killed hatchlings of the Prairie Chicken. In 1973, the legislation banning the release of chemicals to the air prevented all atmospheric and water pollution.
D) Prior to 1993, there was too little genetic diversity in the population and the population declined. In 1993, Prairie Chickens from other populations were introduced to increase genetic diversity, increasing the population size of the birds.