In this task you will be given an answer to a question. You need to generate a question. The answer given should be a correct answer for the generated question.
Q: The Battle of Vimy Ridge was a military engagement fought primarily as part of the Battle of Arras, in the Nord-Pas-de-Calais region of France, during the First World War. The main combatants were the Canadian Corps, of four divisions, against three divisions of the German Sixth Army. The battle, which took place from 9 to 12 April 1917, was part of the opening phase of the British-led Battle of Arras, a diversionary attack for the French Nivelle Offensive.
A: 
when did the battle of vimy ridge start