Answer:
The correct answer is c. parasitic
Step-by-step explanation:
The sexually transmitted infection which is generally not life-threatening are parasitic STIs because most of the STIs caused by parasites are generally remain asymptomatic and they are among the most curable sexually transmitted infections.
For example, Trichomoniasis is a very common STI that is caused by Trichomonas vaginalis a protozoan parasite. It is among the most curable STD and 70% of people infected with this parasite do not even show any symptom. Viral STIs have no cure and bacterial STIs can be fatal some times. So the correct answer is c.