Which is STD responsible for the appearance of a chancre, a small, painless, reddish-brown sore on the mouth or on the sex organs?

The correct option is D

Syphilis

Syphilis, a treatable bacterial disease, is caused by Treponema pallidum. The sexually transmitted disease is transmitted by direct contact with an open sore. It can also be transmitted from an infected mother to her baby any time during pregnancy or at birth. To the child, it can cause heart disease, brain damage, blindness or death. About three weeks after being infected, one or more small, painless, reddish-brown blisters appear on the mouth or on the sex organs. This stage of syphilis is highly contagious. The sores will go away after 1 to 5 weeks, but the disease will not.