The correct option is
B Trichomonas vaginalisLeukorrhea is also a sign of vaginitis (inflammation of the vagina), which is often caused by infection with the fungus Candida albicans or by infection with the protozoan parasite Trichomonas vaginalis. Infection with these organisms may give rise to an irritating discharge that is often quite resistant to treatment. Common symptoms of this disease are burning sensation, itching and discharge of frothy substance, thick, white or yellow mucous.
So, the correct answer is ''Trichomonas vaginalis.