Question: In which month of 1917 did this battle during the World War I, in which Henry Maitland Wilson participated, start?
Sentence (from "Battle of Passchendaele"): The Battle of Passchendaele (German: "Flandernschlacht" , French: "Deuxième Bataille des Flandres" ), also known as the Third Battle of Ypres, was a campaign of the First World War, fought by the Allies against the German Empire.
Relevant evidence: No