Available choices:
a). hydrocarbons;
b). volatile substances;
c). kinetic energy;
d). an area swollen with pus;
e). Chemical energy;
f). competing for resources;
g). add a solute;
h). Positive charges;

Fact 1: Male dogs use pheromones in urine to mark their territory. Fact 2: Generally, pheromones are volatile substances. Given the two facts above, male dogs use what in their urine to mark their territory?
Answer:
b).