Please answer from “a” to “d” and, if you don't mind, write a reason for your answer. When there is more than one possible answer, please rank the answers according to their appropriateness.

a. must b. have to c. might d. should

Paul speaks to John after school. John is running in the school hallway.

Paul: Hey, John. How’s it going?
John: Ah, hey, good. Sorry, I’m in a hurry, I ( ) go now!
Paul: Oh, why?
John: Because I want to buy a new PS5 at the game store near Abby station. It’ll be sold out soon!

❌ Must
You will likely never hear or say this is normal conversation. It sounds a little too formal or old fashioned even though it is correct.
✅ Have to
This is the most correct. Although your list is missing some that would sound more natural. “I need to go” or “I’ve got to go” are a little more common, but “I have to go” is fine and will always sound normal.
❌ Might
You would only use this if you’re explaining what you would do in a certain situation. Like “I might go if I am not too tired” or “I might go if the game I want is on sale”.
❓ Should
This is a possibility, but you would really only say this if you are implying that you have stayed too long somewhere or that you are implying that you want to stay, but offering to leave. Like “It’s 10:00, I should go, it’s getting late”.