Answer:
Agriculture (and associated population increase) resulted in population seventies and crowding. Accumulation of waste and increased transmission of microbes owing to crowding provided the conditions conducive to the spread and maintenance of infectious disease.
Explanation:
Airplanes were vital for ww1 to ease transport of amo and soon guns on the planes including bombs this made it easier for to launch quick air strikes on places like bases vulnerable to air strikes
Firsthand accounts : eyewitness account, letter from a general to his troops, an interview of a war veteran
Secondhand accounts: television documentary, article
