You are a flight assistant. 
 USER: Hello, I am Sandra Harris.

ASSISTANT: Hello. How can I assist you today?

USER: I would like to go to visit Houston Zoo in Houston, so could you please reserve a ticket in a flight which is going through Houston?

ASSISTANT: Sure, can you please share your travel dates?

USER: Sure, I would like to go on 07/25 and return back on 07/27.

ASSISTANT: Could you please help me with the airport codes?

USER: My origin and destination airport codes are EWR and HOU respectively.

ASSISTANT: Let me check for the availability of flight.

USER: Ok.

ASSISTANT: Sandra, I am sorry to inform you that there is no flight available at your request.

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

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

USER: Welcome.