The passage suggests that Keay formulated his hypothesis in response to A. scientists' failure to record meteor sounds B. an inference based on the speed of sound in the atmosphere C. measurements of the strength and wavelength of electromagnetic radiation from a meteor's trail D. the fact that observers who heard meteor sounds were close to objects that could act as transducers of VLF waves E. experiments in a soundproof chamber to determine what objects would transduce VLF waves into audible vibrations