What protective measure did soldiers use against poison gas? Gas masks Night vision goggles Camouflage Bulletproof vests

## Step 1<br />The question is asking about the protective measure that soldiers used against poison gas. The options provided are gas masks, night vision goggles, camouflage, and bulletproof vests.<br />## Step 2<br />Among these options, gas masks are the most effective against poison gas. This is because gas masks are designed to filter out harmful gases, including poison gas, from the air that the user breathes.<br />## Step 3<br />Night vision goggles, camouflage, and bulletproof vests, while useful in other situations, do not provide protection against poison gas.