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

Sentence1: Yes I have a train that leaves at 13:32. Will that do? Sentence2: Yes, if I could please get the reference number. Sentence3: Booking was successful. Reference number is : 3G3X2VLU . Can I help with anything else today? Sentence4: I'm glad I could be of help. Have a great day! Sentence5: That's it! Thank you for your help! Sentence6: Where will you be departing from and traveling to? Sentence7: I need to get a train ticket for friday please. Sentence8: Reference number is : IVX6L3KV . Can I help with anything else? Sentence9: Thank you! Can you please book a room for 1 person for 4 nights, starting Friday, at Hamilton Lodge? Sentence10: Yes. Please book for 1 person. Sentence11: I need to get to Cambridge from Broxbourne and I'd like to leave after 13:15. Sentence12: Will you be needing the reference number? Question: Who has spoken the sentence 4? (A) User (B) System
Answer: (A) User