Final answer:
Spread is the width distribution of projectiles after being fired, and it varies with the horizontal direction of the weapon's muzzle, while range is the maximum horizontal distance traveled by a projectile.
Step-by-step explanation:
The answer to the question is c) Spread. In the context of firearms, the spread refers to the the width distribution of pellets or bullets after being fired from a weapon's muzzle by changing the horizontal direction. This concept is crucial when aiming at a target, as it affects the area that the projectiles can hit. Range is a different concept, which involves the maximum horizontal distance a projectile can travel when launched from a certain elevation and angle, without considering the spread. When discussing trajectories, both the range and spread are key factors in determining the likelihood of a projectile hitting the intended target. By adjusting the spread, a person can manipulate the horizontal dispersion of the projectiles to achieve a desired coverage area, which is directly related to accuracy and effectiveness when aiming.