Explanation:

- Causing miscarriage to B (a woman) by A is specifically addressed under Section 312 of the Indian Penal Code (IPC), which covers voluntarily causing miscarriage.

- Option 1: Murder of unborn child.

- This is incorrect because murder, as per IPC, requires the victim to be a 'person' (someone who has been born). The unborn child does not have this legal status.

- Option 2: Culpable homicide of the unborn child.

- Again, this is incorrect. Culpable homicide is the causing of death to a human being, and the law does not equate causing miscarriage to homicide.

- Option 3: Grievous hurt to B.

- This is correct. Causing miscarriage to a woman, without her consent, is also regarded under 'hurt' or 'grievous hurt' to the woman herself, as per Section 320 IPC.

- Option 4: No offence.

- This is definitely wrong. Causing miscarriage is a criminal offence under IPC, except under certain exceptions (like saving the woman’s life).