I would say there is only 1 answer here :
- I am going to see the dentist tomorrow at 3.
I have an appointment at 3, it means I know exactly when (time and date) I have to go to see the dentist. "Going to do something" is "to have to do something".
Am I right? My English is really limited so I can only explain that much. By the way, my 6th sense tells me to choose the 1st answer, too. :)) When I speak English I do not/cannot always remember all the grammar rules. I often rely on my instinct.
