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- 1. Let us consider the NSA (the non-self-accepting Turing machines) and SA (the self-accepting Turing machines). Which of the following statements is true? a) The NSA is recursive, but not recursively enumerable, and SA is recursively enumerable; b) The NSA is recursively enumerable, but not recursive, and SA is recursive; c) Both NSA and SA are recursively enumerable; d) The NSA is not recursively enumerable (like the set of reals), and SA is recursively enumerable, but not recursive (like the set of positive integers); e) None of the above. Solution The stetement D is correct The NSA is not recursively enumerable and SA is recursively enumerable, but not recursive.