Sex differences in the calling behavior of clawed frogs (Xenopus laevis) can be traced, in part, to hormone-induced changes in the number and type of muscle fibers in the frog's larynx. This illustrates best the way in which hormones influence behavior by means of their effect on
A) muscles and motor neurons. B) changes in social preference. C) sensory or perceptual mechanisms. D) the central nervous system.