Electricity sometimes is used for heating buildings, and nuclear fission is the only method currently used by nuclear plants to generate electricity. Given these facts, which of the following is sometimes  used to indirectly heat buildings among the following options:
- hydrogen and oxygen
 - carbon monoxide
 - direct energy
 - dropping spheres
 - electromagnetic energy
 - a hydraulic system
 - nuclear fission
 - farm animals


 

       nuclear fission  