Correct answer:
¡Buenos días!
If you pass a friend on the street in the morning and your friend says "`¡Hola!" you would respond ¡buenos días! that means good morning! The other sentences doesn't make sense because soy Carlos means I'm Carlos, adiós means goodbye and estoy regular means I'm so-so. Finally, the dialogue could be written as follows:
- ¡Hola!
- ¡Buenos días!