The following diagrams are supposed to represent hypothetical galaxies seen edge-on. The left diagram is a diagram without dark matter, while the right diagram shows a galaxy with a dark matter halo. Consider the force of gravity on the stars shown in the figures ( which you can assume all have the same mass):

    A ) Star A should be moving faster than star C because the dark matter will slow star C down
    B) Star C should be moving faster than star A becuase the extra gravity from the dark matter will exert a greater force
    C) Both stars A and C should be moving at the same speed, because the dark matter has no effect
    D) You can't tell from the information given which star is moving faster

When called for, hold up the letter of your choice.