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: We have the bridge guest house which is moderately priced and the lensfield hotel which is expensive, would you like me to book you for either one? Sentence2: Yes the train should go to cambridge and should leave after 18:30. Sentence3: I have several available. What days would you like to stay? Sentence4: Sure, Are you traveling to cambridge? What time would you like to leave or arrive by? Sentence5: Either one is fine. I want it for 6 people for 2 nights starting wednesday. Sentence6: Thank you. Yes, I think I'll be traveling by train wednesday as well. Are there any trains leaving ely on that day? Sentence7: I recommend train TR0328. It departs at 19:35 and will get you there by 19:52. Want me to book it? Sentence8: I do not have any hotels in the east with a 3 star. Would you like to try something else? Sentence9: I'm looking for a place to stay in the east. Sentence10: Ok I was able to book your party at Bridge Guest House. Your reference code is ZUFSD1J5 . Is there anything else I can help you with tonight? Sentence11: Not right now, thanks. What's the total travel time for that train, though? Sentence12: Safe travels and if you need anything else, please contact us. Sentence13: I don't need to book it. I need a 3 star in the east. Sentence14: I believe that's it. Thanks so much for your help! Sentence15: It's a quick, 17-minute trip. Is there anything else I can help you with today? Sentence16: Can you find something in the south? Question: Who has spoken the sentence 4? (A) User (B) System
Answer: (A) User