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

Sentence1: I really do not have a preference on the area. Which one would you recommend? Sentence2: We have a large number of colleges, could you tell me the area you would like to visit one in? Sentence3: christ's college is free and located in the centre. Would you like anything else today? Sentence4: The booking was successful. Your reference number is: DKI36RGY . Is there anything else I can do to help you today? Sentence5: Okay, I'm glad to have assisted you today! Sentence6: A red volkswagen is booked. 07772378395 is the number. Do you need more help? Sentence7: The phone number is 01223334900 Sentence8: Actually, yes. I wanted to visit a college whilst I'm in town. Could you recommend one for me? Sentence9: There are many options that are 4 star. Is there a particular area or price point you would like to stay in? Sentence10: That is all I need, thanks. Sentence11: Hi, I'm looking for a guesthouse. Do you know of any 4-star properties? Sentence12: Acorn Guest House located in the North is a 4 star location with free parking and wifi, would that suit your needs? Sentence13: I will also need a taxi between them. I need to leave the hotel by 24:45. Sentence14: Can you give me the phone number for it? Sentence15: No particular area but free parking would be nice Sentence16: Yes please book that for 5 people for 3 nights starting on Saturday. Question: Who has spoken the sentence 15? (A) User (B) System
Answer: (B) System