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

Sentence1: Booking was successful, the total fee is 8.8 GBP payable at the station. Reference number is : T4I7L6BG . Can I help with anything else today? Sentence2: Alright, thank you, I think that will be all for today. Sentence3: There are 6 trains leaving that will get you there by 16:45, the closest TR3240 arriving at 15:52. Would you like to make a reservation? Sentence4: What time you like to leave? Sentence5: Yes please, thank you for your help. The reference number will come in handy. Sentence6: I can help with that! There are a total of 42 trains departing from Ely. What is your destination so I can narrow this down for you? Sentence7: The Hotpot sounds great! Can you please make a reservation for Friday for 2 people at 8 pm? Sentence8: I'm also looking for a expensive restaurant in the north. Sentence9: I would like to go to cambridge on thursday Sentence10: I am looking for a train departing ely and should arrive by 16:45. Sentence11: You're welcome. Let me know if there is anything else I can help you with. Sentence12: Choose your favorite. I do need an address and post code, please. Sentence13: Sure, do you have a food preference? I see Chinese, French, European and Asian Oriental. Sentence14: Again, thanks for all of your help today. Good bye. Sentence15: Sure! Your reservation at the hotpot for Friday for 2 people at 8 pm is successful. Would you like a reference number? Sentence16: How about The Hotpot? It is located at 66 Chesterton Road Chesterton and the postal code is cb41ep. Sentence17: I'm sorry at the moment I can not obtain that for you. Sentence18: Yes, please make me a reservation for two people on TR3240 arriving at 15:52. Sentence19: It doesn't matter what time I leave as long as I'm there by 16:45. Sentence20: You're welcome, have a nice day. Question: Who has spoken the sentence 4? (A) User (B) System
Answer: (A) User