The corn blight of 1970 was brought under control by:

a. crossing highly uniform U.S. corn varieties with genetically diverse ancestral varieties from Mexico.
b. strange weather patterns resulting in a drought that killed the fungus.
c. the accidental release of a genetically engineered fungus from a research lab.
d. repetitive treatment with various chemical sprays.
e. pollution that seemed to have a greater adverse effect on the corn blight fungus than on the corn itself.