What Was One of the Main Reasons for an Increase

What was one of the main reasons for an increase in gonorrhea just prior to the 1980s?

A) Gonorrhea has always increased during wartime activity.
B) Gonorrhea mutated and was no longer curable with antibiotics.
C) The shift from the use of the condom to the use of the contraceptive pill which increases a woman's susceptibility to gonorrhea.
D) The fact that neither the male nor the female experience any symptoms from gonorrhea.