You are presented with the question "One of the oldest forms of energy used by humans can be used to produce what?" and the following answer choices: 
- food
 - engines
 - waves
 - chemicals
 - Decibels
 - sound
 - energy
 - hormones

Now knowing that tidal energy can be used to produce electricity and tidal energy is one of the oldest forms of energy used by humans, choose the best answer.


 

       energy  