He was more depressed than ever as he drove on by himself. The late afternoon had grown hot and sultry and the country had flattened out. Deep in the sky a storm was preparing very slowly and without thunder as if it meant to drain every drop of air from the earth before it broke. There were times when Mr. Shiftlet preferred not to be alone. He felt too that a man with a car had a responsibility to others and he kept his eye out for a hitch-hiker. Occasionally he saw a sign that warned: "Drive carefully. The life you save may be your own." Which statement most accurately represents the excerpt's larger idea?