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"): Passchendaele lay on the last ridge east of Ypres, 5 mi from a railway junction at Roulers, which was vital to the supply system of the German 4th Army.
Relevant evidence: No