a. an electron is orbiting the nucleus of an atom
b. a flea walking at a constant speed on a dog's back
d. a Honda Prius moving at 70 mph
Momentum can be defined as quantity of motion present in a body. It is also called "mass in motion." All objects have mass so if an object is moving, then it has momentum. In terms of an equation, the momentum of an object is equal to the mass of the object multiply by the velocity of the object.
So in conclusion, option a, b and d having momentum.
Learn more about mass here: https://brainly.com/question/19385703