You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, do you need any help from us?

USER: I planned to meet my friend in OAK, can you please help me to book a flight ticket from ORD?

ASSISTANT: Sure, could you please share your departure and arrival day?

USER: I prefer to travel on Sep 21 and Sep 23.

ASSISTANT: Ok, could I have your name please?

USER: I am Elizabeth Davis.

ASSISTANT: Ok, do you need direct or connecting flight?

USER: I prefer to travel in a connecting flight.

ASSISTANT: Ok, do you have any other specifications?

USER: I would like to travel in economy class. I would like to travel in business class.

ASSISTANT: Sorry, there is no flight with your requested class.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thank you for consulting us, have a great day.