You know that an object has momentum if
Ait has a force acting on it.
Bit has mass and a force is acting on it.
Cit has mass and its position is changing.
Dit is stationary and has a force acting on it.
Ait has a force acting on it.
Bit has mass and a force is acting on it.
Cit has mass and its position is changing.
Dit is stationary and has a force acting on it.