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: Ok. I can help you book a taxi from Scudamores Punting. Where do you want to go from there? Sentence2: Yes, are there any kind of boat tours available through town? Sentence3: Great! I have booked your taxi, which should be a White BMW and its contact number is 07719541714. Sentence4: I'd like to stay on Wednesday, Thursday, and Friday, please. Is that available? Sentence5: To my hotel. Sentence6: In the centre of town, if possible. Sentence7: I'm looking for a guesthouse that offers free parking. Sentence8: There are a few. Do you care what part of town? Sentence9: It was a pleasure assisting you. Enjoy your stay. Sentence10: May I assist you with anything else today? Sentence11: I have many options available. Would you like to stay in a particular area of town? Sentence12: Of course! When would you like to stay? Sentence13: The aylesbray lodge guest house meets all of your requirements and has a 4 star rating. Would you like me to book a room? Sentence14: That's all I need. Thanks Sentence15: Yes, actually I prefer to stay in the south part of town. And I would love something that offers free wifi. Sentence16: Great! Your room has been booked for 3 nights starting Wednesday and your reference number is NVZNJX13 . Is there anything else that I can help you with? Sentence17: Yes, could you make a reservation for 8 people, please? Sentence18: Great, thank you! Sentence19: Yes there are two companies that offer boat tours in the centre of town, Scudamores Punting and The Cambridge Punter. Would you like more information? Sentence20: Sure but I also need to book a taxi to leave the attraction by 6:45. Question: Who has spoken the sentence 15? (A) User (B) System
Answer: (B) System