Sexually transmitted diseases $(STDs)$ cannot be transmitted easily during the use of which of the following?

Which of the following principles are used to prevent $STD$ infection?
$(i)$ Avoid sex with unknown partners
$(ii)$ Use condoms during coitus
$(iii)$ Blood transfusion
$(iv)$ All of these

Which of the following is an $STD$?

In the following STIs, which one is not completely curable?

Early symptoms of most $STDs$ are: $I$. Itching,$II$. Fluid discharge,$III$. Slight pain,$IV$. Swelling. Choose the correct option.

The test for 'syphilis' was developed by