The aircraft played a key role during the First World War. Initially, it was used for the transport of soldiers as well as for reconnaissance. Namely, the enemy trenches were easily visible from the planes and information about the position of the enemy trenches became available. The Germans, however, invented the "interrupter", which allowed the machine gun to synchronize with the propeller. In this way, the air fight was improved when a pilot could hit a pilot of an enemy aircraft or cause losses to the enemy army at a slightly lower flight. But after all the sides realized that the plane could be used to fight the enemy outside the battlefield, the bombing of military and industrial targets on land began, far beyond military action, which caused huge civilian losses.
The answer is a.
