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: Of course! Thanks, good bye. Sentence2: That restaurant serves chinese food and is expensive. Sentence3: Thank you for your help, good day. Sentence4: Great, I have booked that for you and your reference number is XDYJMTO7 . Sentence5: welcome again next time. enjoy our services Sentence6: I'd like to book a table for 3 people for saturday at 1815 please. Sentence7: Help me find a restaurant called hakka please Sentence8: You as well. Thanks for using the service! Question: Who has spoken the sentence 4? (A) User (B) System
Answer: (A) User