Explanation:

- Option 1: The offence of murder

Murder involves the intentional killing of another person. A, in this scenario, did not actively cause B's death.

- Option 2: The offence of abetment of suicide

Abetment of suicide involves inducing someone to take their own life. A's inaction does not fit this description.

- Option 3: The offence of culpable homicide not amounting to murder

This involves causing death without the intent required for murder. Inaction alone typically doesn't constitute this offence.

- Option 4: No offence

For an act to be illegal, there usually must be a statutory duty to act. While A's behavior might be morally questionable, legally, there is no offence if there is no duty to act.