You are shown a conversation between a user and system. Identify who has spoken the indicated sentence based on the conversation.

Sentence1: Great. Now I need somewhere to stay. I want an expensive place with 2 stars plus parking and wifi too. Sentence2: express by holiday inn cambridge is the only available hotel we have. Would you like me to make the reservation? Sentence3: 1 person and 12:15 on Sunday or Thursday. I also need a reference number Sentence4: Could you try again, just want something on Thursday, at 12:15. Sentence5: Yes, I'd like to find one in the centre. Sentence6: I am looking for an expensive Indian restaurant. Sentence7: How about the curry garden that is in the centre of town and serves indian food? Sentence8: Neither of those days seem to be available. Would you like me to try a different restaurant. Panahar is expensive and in the same area. Sentence9: There seems to be an error in the restaurant booking system. Do you need anything else, like a hotel or taxi in the meantime? Sentence10: Thanks for letting me assist you today. Enjoy your trip! Sentence11: Is Curry Garden expensive? If so, I want to make a reservation for Sunday. Sentence12: Yes it is expensive. Their address is 106 Regent Street City Centre. How many people shall I reserve it for and at what time? Sentence13: I can reserve a table for 1 on Thursday at 12:15. Should I book it for you? Sentence14: Yes, please, for 4 people, 4 nights. Same day as the restaurant booking. Sentence15: There are several options, is there a specific area you prefer? Sentence16: Could you please try again? I really need that reservation. I'd prefer it for Sunday but if they can't accommodate that time, Thursday will suffice. Sentence17: No thank you, you have been very helpful but please use you're and your in the right places. Sentence18: Your all set, the reference number is 6BRFT2OA, is there anything else I can do for you today? Sentence19: Good news, the booking system finally worked and I made the reservation! Your reference number is I3VJP80T Sentence20: Yes I already asked you to do it!! And send the reference number! Question: Who has spoken the sentence 15? (A) User (B) System
Answer: (B) System