C is standardised, so it's straightforward to
teach standard C.  But
 you can't teach "standard Lisp" without picking a standard: CL or
 Scheme (and then which Scheme standard?) 
You can't teach "standard C" without picking a standard, too.  There
are at least three (K&R v1, ANSI C, and C99) and probably more that I'm
not aware of or which don't come to mind immediately.  "The wonderful
thing about standards is there are so many to choose from!"
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