If a language L1 is polynomially reduced to the language L2 and L2 is polynomially reduced to the language L1, then which of the following cannot be TRUE?
- L1 is decidable and L2 is undecidable.
- L1 is regular and L2 is CFL.
- L1 is recursive and L2 is recursively enumerable.
- L1 is decidable and L2 is decidable.