Find the odd number / letters / word from the given alternative:

The answer is D. Pistol : Gun.

A church is a building for religious activity, a monument is a structure built to commemorate a person or event, a car is a vehicle for transportation, and a bus is a large vehicle for public transportation. A pistol is a small firearm, while a gun is a larger firearm.

Pistol and gun are both firearms, but they are different in size and power. A pistol is a small firearm that is typically held and fired with one hand, while a gun is a larger firearm that is typically held and fired with two hands. Pistols are typically used for self-defense or target shooting, while guns are typically used for hunting or warfare.

In the given options, all the other words are related to each other in a way that pistol and gun are not. Church and monument are both structures that are built to commemorate something, car and bus are