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: The hamilton lodge is moderately priced and has 3 stars. Would you like to make reservations? Sentence2: Really makes no difference to me as long as its on the North side of town Sentence3: I need to find a train leaving Cambridge and going to Ely. Can you help? Sentence4: The train leaves ely at 19:50. Would you prefer a guesthouse or hotel? Sentence5: no that is all thanks Sentence6: There is the TR6053 that arrives by 20:07. Do you want me to book it? Sentence7: Can you confirm if the hamilton lodge has both free parking and free wifi? Sentence8: Yes, the hamilton lodge has free parking and wifi. Would you like me to book? Sentence9: You can book TR6053 since it is only a 17 minute trip. Thank you Sentence10: I will take any suggestions you have. Sentence11: You are welcome. It was a pleasure serving you from Cambridge TownInfo centre. Goodbye. Sentence12: I have about 11 different places so far. Do you have a certain price range in mind? That may help narrow it down some. Sentence13: No, not today. I just needed information. Sentence14: I can help! There are many options Sentence15: No problem, anything else besides the hotel and train today? Sentence16: I need to leave on Friday and arrive by 21:45. Sentence17: What's the travel time on that one? Sentence18: What time does that train leave Cambridge? I also need a place to stay in Ely, with free parking and free wifi? Question: Who has spoken the sentence 15? (A) User (B) System
Answer: (B) System