Why was the piece of equipment in the photo necessary for both sides in world war i
a to protect the soldiers from diseases
b to protect the soldiers from poisonous gas
c to protect the soldiers from flamethrowers
d to protect the soldiers from machine gun-fire

I need the picture in order for me to answer but i beleive chemical warfare was used a lot in ww1 so it would make sence it was a gas mask and if it was then it would be B to protect the soldiers from poison gas. whole cities had gas mask in case of a bombing including is schools too.

For national parks/forests;