Question about monsters with multiple attacks

[Stalker0]

This one is mainly stemmed at those who got to try the dragon fight at DDX.

The entry showed three attack modes: bite, claw, and double claw.

Does the dragon use all or one of these modes at a time? Does he use the first entry (bite) for his opportunity attacks?

 

[ThirdWizard]

As I understand it, opportunity attacks are done with the attack that has a sword with a circle around it (or the lowercase "m" in many of the stat blocks).