Which of the following statements is false?

The statement in option D is false because not every subset of a recursively enumerable set is recursive. While recursively enumerable sets are those recognized by Turing machines, subsets may not be decidable (recursive). For example, the halting problem is recursively enumerable but its subsets are not necessarily recursive. The other options are true: NFAs can be converted to DFAs, non-deterministic Turing machines have equivalent deterministic versions, and all regular languages are context-free. Thus, D is the false statement.