Show allows any option that can be applied to graphics to be given.
Options explicitly specified in Show override those included in the graphics expression.
Show[g1, g2, ...] or Show[{g1, g2, ...}]concatenates the graphics primitives in the gi, effectively overlaying the graphics.
The lists of non-default options in the gi are concatenated.
Show applies the function defined as the setting for DisplayFunction, and returns the result. For ordinary notebook operation, this function is just Identity.