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

Sentence1: No, that's all I need today. Thank you so much. Sentence2: I need to leave after 09:15, please. Sentence3: How about bridge guest house? They are moderately priced with free wifi and parking and 3 stars. Sentence4: Absolutely! What time do you need to arrive by? Sentence5: Your train has been booked for 6 people. The train ID is TR2083. Your reference number is WCVY3PV1 . Sentence6: You have a few options available if you're traveling from bishops stortford to cambridge. There is a train leaving at 09:29, Does that work for you? Sentence7: That sounds great. Can I book 2 nights for 6 people starting on Friday. Sentence8: Thanks. I'm also looking for information on moderately priced hotels with free wifi. Sentence9: No I do not. Sentence10: Do you have a preferred area of town? Sentence11: I have you booked, the reference number is VM1KGTU7, can I help with anything else? Sentence12: Great. Let's book it for 6 people. Give me the reference number. Sentence13: I'm sorry. Nothing is coming up for your specifications. I need you to narrow down your info. Sentence14: The place must have a 3 star rating and include parking. Sentence15: You have 17 options that meet that criteria. Would you like a recommendation or do you want to narrow your options down? Sentence16: Well lets try again and book me in what you choose for 2 nights from Friday for 6 people. Sentence17: Thank you for calling. Enjoy your trip! Goodbye! Sentence18: Can you help me find a train that leaves on friday departing from bishops stortford? Question: Who has spoken the sentence 15? (A) User (B) System
Answer: (B) System