Explanation:

- Voluntary drunkenness generally is not an excuse in criminal law.

- Option 1: Delirium Tremens

- Delirium tremens is a severe form of alcohol withdrawal, often with confusion and hallucination. If it causes insanity, it could be an excuse, but not mere drunkenness.

- Option 2: Where a specific intent is an essential element of an offence

- If the offence requires specific intent (for example, theft needs an intent to steal), and voluntary drunkenness made it impossible to form such intent, it may be considered as an excuse.

- Option 3: Both (a) and (b)

- This adds both aspects together. However, *only specific intent offences* are excused, not mere drunkenness leading to delirium tremens—unless it amounts to insanity.

- Option 4: None of the above

- This option rejects all excuses for voluntary drunkenness.

Correct Answer: Option 2: Where a specific intent is an essential element of an offence.