C. is the answer.
Let's break it down:
a. Light = energy. When you turn off the lights in your house, you are conserving energy.
b. Heat=energy. Turning down the heat in your house saves energy as well.
c. Long, hot showers use a lot of energy, and there's nothing in the answer option to make us think this is conserving energy.
d. A fuel efficient automobile will use less fuel over time, which contributes to conserving energy.
Hope this helps!
