Answer:
D: Whether to reunify with the rest of Ireland.
Explanation:
The violence has arosed from conflict over wheter to leave the United Kingdom and form the United Ireland, or staying in the UK. Most of the population is in favor of staying in the UK, but there are many nationalists that want to reunify with the rest of Ireland, which leads to violence.
The correct answer is:
D: Whether to reunify with the rest of Ireland.