You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I help you?

USER: Margaret Wright here. Please help me out in booking the ticket from DFW to AUS.

ASSISTANT: Sure, may I know your trip dates please?

USER: My trip dates will be Dec 19 to Dec 21.

ASSISTANT: Do you have any other requirements?

USER: My return time must be in the evening.

ASSISTANT: Ok, please wait.

USER: Ok.

ASSISTANT: Sorry, we regret to inform you that there is no flight available as per your request.

USER: That's ok, thank you.

ASSISTANT: My pleasure.