As the velocity of an object increases, so does its energy. What does this imply?
a) At very low velocities, the object's energy is equal to its mass times $c^{2}$.
b) In order for an object with mass $m$ to reach the speed of light, infinite energy is required.
c) Only objects with $m=0$ can travel at the speed of light.
d) all of the above
e) none of the above