PCR is commonly used in research, forensics, and for the diagnosis of pathogens and genetic diseases. A commercial standardized diagnostic PCR test has been developed that uses one set of primers to amplify a short DNA template. For which scenario would such a standardized PCR test be most appropriate

The correct answer is A

 HIV can't be transmitted by shaking hands, using the same plate
It can only be transmitted by blood. So that means as well during sexual relations, because in the vagina , the "skin" is very thin and there are many blood vessels
By semen, if your partner has the HIV and doesn't use condom, he is a criminal if he didn't tell you anything, unless himself doesn't know.

That's why the use of condoms , even if a woman is under contraception, should be always used. If the relation last, each does the test, and if each is truly  respectful, you can stop using it

Among the youngest, there is again a higher number of HIV because there are less prevention than a few years ago