First, who and where is cless? And how do you get the scenes to trigger with the nurses?
Cless is a teacher in the college, look there, then to start the event take the nursing class (<--- That might not be the actual name), a 3rd option you pick that will appear when you see Cless. For Sana and Miki you would have to first, trigger the event with Cless, take the biology class, then when the encounter happens don't doge.