Fact 1: Some touch receptors sense differences in temperature or pain.

Fact 2: Temperature Temperature is an measurement of the amount of heat.

Given the two facts above, answer the question "what do some touch receptors sense differences in?" with the following options: 
- voltage
 - visible energy
 - fingers
 - refraction of light
 - gravity shifts
 - amount of heat
 - the skin
 - change in density


 

      amount of heat   