1- Aha, I've discovered the secret door.
2- Carla, would you please move over?
3- Both egrets and herons nest here.
4- How can we best solve the problem?
An interjection is a word used to express a particular emotion or sentiment. Here, the only sentence that contains an interjection is 1 - Aha, I've discovered the secret door. Aha is the interjection.
