Cytologic smears are useful for diagnosing which of the following?

Cytologic smears are most commonly used for detecting viral infections, sexually transmitted infections and fungal infections. Therefore, options B and C are incorrect as they do not match with the types of infections that are detectable using cytologic smears. Option D is also incorrect, as HPV and Gonorrhea are bacterial infections, whereas cytologic smears are more effective in detecting viral infections. Option A is the correct answer since Candidiasis and Herpes Simplex are both viral infections that can be diagnosed using cytologic smears.