Rifles, shotguns, and handguns differ mostly based on their: a. barrels and b. ammunition

Option:  a. barrels

Explanation:

Different types of guns are distinguish through the size of their barrels. A barrel is a long metal tube with hollow inside that allows bullets to pass when fired. Usually, large barrels allows bullets to hit the target more often without missing it. The shotguns use for hunting animals and often use to shoot small and fast-moving targets. Handguns also are known as pistols, which are smaller in size compared to the others.