Turing decidable == Recursive languages, which are closed under complementation. So, $I$ is True.
The Turing decidable (ie recursive) languages are divided into three classes:
- P (Polynomial time)
- NP (Non-deterministic polynomial time)
- P Space (Polynomial space)
Generally, we consider only two of these classes — P and NP.
They're subdivisions of the decidable zone, so definitely if a language is in NP or P or P space, it is decidable. $III$ is True.
Option D