You are presented with the question "A method of heating a building might be what?" and the following answer choices: 
- dangerous
 - Blizzards
 - Heated arguments
 - threatened
 - major threat to health
 - Direct sunlight.
 - Mothballs
 - slow and inefficient

Now knowing that energy is used for heating a building by a heating system and passive solar thermal energy involves heating buildings using direct sunlight, choose the best answer.


 

      Direct sunlight.   