Question

How would you say good-bye to a friend whom you might not see for a long time?

Answer 1

D. ¡Adiós!

Adiós means “goodbye” which is more final than just saying “bye” or “Hasta luego”

Hasta pronto and Hasta ahora both mean that you will see them soon

Hasta mañana means see you tomorrow

Answer 2

D. ¡Adiós!

Adiós is a more formal way of saying goodbye, which you would use in that case (a friend you don't see for a long time).

Hasta luego - see you soon
Hasta pronto - see you soon
Hasta ahora - see you soon
Hasta mañana - see you tomorrow


Hope it helped!