Fact 1: Male dogs use pheromones in urine to mark their territory.

Fact 2: Generally, pheromones are volatile substances.

Given the two facts above, answer the question "Male dogs use what in their urine to mark their territory?" with the following options: 
- hydrocarbons
 - volatile substances
 - kinetic energy
 - an area swollen with pus
 - Chemical energy
 - competing for resources
 - add a solute
 - Positive charges


 

  volatile substances       