Hello Nancy! I agree that B is the correct answer as that is the past tense form of "promise". If you were to use "promises" then you would have to add the following: "...promises to come tomorrow". This time the verb is in the third person present tense and is an assurance that it will be happening. I hope that helps!

B. promised

Thanks a lot, Michael and Valeriya. But my teacher told me that present perfect tense implies something that happened in the past results in some present action or thoughts. It must have something to do with the present. For example, A: Why are you still waiting here? B: My mum has promised to come to my party. My teacher said if the former use the present tense, the later should use the present tense, too. Or it may sound awkward. For instance, A: Are you hungry? B: No, I had my dinner an hour ago.(That is not right. It should be ' No, I've had my dinner.') So, I think if I use the present perfect in the question I asked, it means ' Nancy promised to come. So I am waiting until she comes.' That makes sense, too. Would you please tell me if I am right? I am always confused about the simple past and the present perfect tense.

This is interesting - it really shows up the difference between simple-past and present-perfect. When person A says that Nancy is not coming, that means the question of her coming is decided. So it's a job for the simple past. A different situation would be A: Is Nancy coming tonight? B: I expect her to. She has promised. In this situation the question of whether she will come is still undecided, so it's present perfect. The question might also be decided by her arrival, which again means the simple past is used: A: Hey look, Nancy has arrived! B: Ah, good, she promised she would come.

This is a question to test your knowledge about when to use the simple past tense, and when to use the present perfect. It might help you to review the information at this link: https://www.perfect-english-grammar.com/present-perfect-or-past-simple.html