Given the task definition and input, reply with output. You are shown a conversation between a user and system. Identify who has spoken the indicated sentence based on the conversation.

Sentence1: Yes I need it to go to cambridge, is that possible? Sentence2: Booking was successful. The table will be reserved for 15 minutes. Reference number is : AYQO5ZTE . Can I help you with anything else? Sentence3: We have 2 trains that match your criteria - the TR0788 that leaves at 05:32 and the TR0605 that leaves at 06:32. Which one should I book for you? Sentence4: wednesday and I want to get there by 08:00 leaving broxbourne, how much is that? Sentence5: Do you need a taxi? Sentence6: Have a great day. Good bye. Sentence7: The trip will cost 17.90 pounds. Sentence8: I am planning a trip in Cambridge. Sentence9: what area please and how many tickets Sentence10: We have several great options, most of which are in the center of town. My favorite is Caffe Uno. Sentence11: No, I don't need it booked. What's the price for the TR0788? Sentence12: Sounds great. I need a reservation for 1 on Wednesday at 15:30 Sentence13: Yes, I am happy I could assist. Sentence14: The price is 17.90 pounds. Can I help you with anything else today? Sentence15: Okay, how can I help you? Sentence16: No that is it, thank you! Sentence17: im looking for an expensive restaurant that serves italian food Sentence18: I will also need a train Question: Who has spoken the sentence 15? (A) User (B) System
Answer: (B) System