Insulating materials are rated by their specific heat heat index r-value temperature resistance

Option (c) is the correct answer.

Explanation:

The difference in temperature when per unit of heat flux is required by one unit of heat flux between a barrier of warmer and colder surface present in steady state condition is known as R-value.

Mathematically,       R-value =

Thermal resistance of insulating products or materials can be known with the help of R-value. As more is the r-value of a substance more will be its insulating power.

Therefore, we can conclude that insulating materials are rated by their r-value.

causes

fossil fuels burn

cities become more industrialized

human population grows worldwide