Explanation:

- Extortion: This involves obtaining something through coercion or threats. In this case, there is no evidence of force or threats used to obtain the cigarette, so this option doesn't apply.

- Criminal Breach of Trust: This involves violating someone's trust, particularly in situations where property or responsibility was entrusted to someone. Dropping a brass disk into a cigarette vending machine doesn't involve trust or entrustment, so this isn't applicable.

- Theft: This involves dishonestly taking property with the intent to permanently deprive the owner of it. Using a brass disk to obtain a cigarette without proper payment could be seen as theft, as the intention is to unlawfully take a cigarette without paying.

- No Offence: This implies that no laws have been broken. Given the deception involved, this option seems unlikely since there is an element of intent to acquire goods without payment.

Correct Answer: Theft - The act of using a brass disk to fraudulently obtain a cigarette fits the definition of theft, as there is dishonest intent to unlawfully obtain property.