6. If energy is conserved, why do we speak about "running out of energy'' or having an "energy shortage" or
A. Energy is not really conserved
B. Energy is difficult to find.
C. When we use energy, we convert it to a more disordered, diffuse form that cannot be easily reused.
D. Energy does not have a precise definition in physics, but in our everyday language it does have a precise definition.
E. There are not sufficient sources of work.