C) An unbalanced force is acting on the car in the direction east
One reason that it would be appropriate to talk on your cell phone, could be reporting an accident. For instance, a car crash, a sign in the road anything regarding safety of drivers.
The speed of a mechanical wave depends on the mechanical properties
of the medium through which the wave is traveling.
The speed of an electromagnetic wave depends on the electrical properties
of the medium through which the wave is traveling.
It's pretty well unanimous for choice <em>A</em> .