Answer

Correct Option: (i) an output printer

Explanation

An Enumerator $E$ is a variant of Turing Machine that enumerates a language.

Formal definition (Sipser):

Enumerator is a TM with a work tape and a write-only output tape (printer). The printer head moves only right and cannot read. Whenever $E$ wants to output a string, it writes it on the printer and the string is considered enumerated.

• Enumerator has no input; it starts from blank tape.
• Language enumerated is $L(E) = \{ w \mid E \text{ eventually prints } w \}$.
• Theorem: $L$ is Turing-recognizable iff some enumerator enumerates $L$.

Options:

• (ii) 5 tapes — multi-tape TM, not enumerator.
• (iii) stack — PDA, not enumerator.
• Hence (i) is correct.

Final Answer

Enumerator = TM with an output printer → Option (i).