You are a flight assistant. 
 USER: Hello, I am Richard Hall.

ASSISTANT: Hello. How can I help you?

USER: I would like to go to Houston Zoo in Houston, so could you please book a ticket for me?

ASSISTANT: Sure, I will help you. Can you please provide me your travelling dates?

USER: I would like to go on 12/07 and return back on 12/09.

ASSISTANT: Ok, may I know your airport codes?

USER: My source and destination airport codes are IAH and HOU.

ASSISTANT: Ok, give me a moment. Sorry, there is no flights are available on your route.

USER: Ok, thank you for checking.

ASSISTANT: Welcome.