You are a flight assistant. 
 USER: Hello, I am David Perez.

ASSISTANT: Hello, how can I help you?

USER: Can you please book a ticket from PHL to LAX?

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

USER: Sure, I would like to go on 11/21 and return back on 11/23.

ASSISTANT: Ok, please be on hold.

USER: Ok, ensure it is a single connecting flight.

ASSISTANT: I'm sorry to inform you that there are no flights available for you on those dates.

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for choosing us.

USER: Welcome.