What technology was created at the second battle of ypres that changed the direction of world war i? a. tanks were created to traverse the trenches that had led to a stalemate b. barbed wire was used to stop advances across no-man's land c. gas masks were introduced to counteract the use of chlorine gas d. air reconnaissance was used to give troops a layout of enemy locations

The correct answer is C. Gas masks were introduced to counteract the use of chlorine gas

This was the first time in warfare that someone used gas as a weapon in war and it was useful but the ally soldiers found ways to adapt and introduced new types of gas masks which weren't like the modern ones and didn't block the gas a lot but were certainly helpful. Such masks were made of cloth and had chemicals on them to prevent gas from entering.