Energy is used for heating a building by a heating system, and passive solar thermal energy involves heating buildings using direct sunlight. Given these facts, a method of heating a building might be what among the following options:
- dangerous
 - Blizzards
 - Heated arguments
 - threatened
 - major threat to health
 - Direct sunlight.
 - Mothballs
 - slow and inefficient


 

      Direct sunlight.   