Which shows the need for gene banks for agriculture crops a . plagues wiped out the entire crop in a large region b. global warming caused reduced rainfall in an agricultural area c. volcanic eruptions formed new land d. soil erosion increased due to poor farming practices

The answer is A) Plagues wiped out the entire crop in a large region. This would result in the dramatic lowering of genetic diversity within the crop species. This as we know is very bad for an organism, as a lower genetic diversity can result in deleterious genes becoming more common, which can dramatically lower the fitness of a species. By storing genetic information for cop species in a gene bank, we can maintain the wide genetic diversity of important crop species, in case some sort of disaster happens to wipe out much of the crop population within a particular year. 

Oh dog