we use if in the place of a question word.
ตัวอย่างเช่น Do you know if Mona is coming to the meeting?
I’d like to know if I can pay online.
Thanking
Thanks.
Thank you very much for you hospitality / all your hard work / the lovely dinner.
Farewells
I really must be going.
Have a safe flight.
Take care.
I’ll be in touch.
I hope we can work together again sometime / meet again sometime.