Fact 1: When electricity flows to a light bulb , the light bulb will turn on.

Fact 2: Materials that control the flow of electricity are called resistors.

Given the two facts above, answer the question "What could prevent a light bult from turning on?" with the following options: 
- sensory neurons
 - herbicide
 - A resistor
 - focusing a lens
 - evaporation
 - heat energy
 - heating liquids
 - energy barrier


 

   A resistor      