In a TV Tube, the Picture Is Created by a Beam

Multiple Choice

In a TV tube, the picture is created by a beam of electrons that travels down the tube at a very high speed. What is the mass of one of these electrons, compared with an electron at rest?

A) The mass of an electron is measured to be the same regardless of how fast it is moving.
B) The moving electron appears to have a smaller mass.
C) The electron appears to have a greater mass if one is in front of the tube (electrons approaching) and a smaller mass if one is standing behind the tube (electrons moving away) .
D) The moving electron appears to have a greater mass.