They formed a strong union.

They allied to counter the enemy.

This car drives automatically.

Exercising every day is important for maintaining health.

An intransitive verb represents the action or state of the subject, and does not require a direct object.

He is undergoing training for extravehicular activity.

He engaged in an extravehicular activity from the spaceship.

Mollusks often have hard shells to protect their soft bodies.

He underwent surgery for esophageal cancer.

His artery appears to be healthy.