As a car heads down a highway traveling at a speed v away from a ground observer, which of the following statements are true about the measured speed of the light beam from the car's headlights? (select all that apply.)

a. the ground observer measures the light speed to be c.
b. the driver measures the light speed to be c.
c. the driver measures the light speed to be c − v.
d. the ground observer measures the light speed to be c + v.
e. the ground observer measures the light speed to be c − v.