Answer:
A. First incubation at 37 Celsius; second at room temperature
Step-by-step explanation:
When you are sick for some sort of infection your body will raise your body temperature to kill the infection (bacterias, viruses). 37 C it's normal temperature and those pathogens can easily grow up (very fast). 15 minutes it's enough to promote the bacteria reproduction at 37 C, to decelerate you need to change the temperature (a lower one just to decrease the reproduction rate).
Having a low rate reproduction of bacterias it's fine for your culture media, it will last for more time than a culture media with 37 Celsius all the time.