Select the first line and click the New Group button.

A new Group appears at the end of the list.

You’ll use the new Group to randomly choose either the Arpeggio, Piano, or Rhythm part. You can move those objects out of the first Group and into the newly created Group by dragging them below the new Group.

One at a time, drag each of the objects, except the Explore-Theme, into the newly created Group.

Because the default Group at the top of the list is set to Random Continuous, a circumstance is created where either the Explore-Theme is played or the new Group you just created plays continuously through its list. To achieve the desired effect, you need to adjust the Group playback conditions. The first Group should be set to Sequence Continuous so that once the Explore-Theme Music Segment plays, it will then move to the Group that contains the remaining Music Segments.

Change the first Group back to Sequence Continuous and then play the Explore Music Segment.

You hear that the Explore-Theme immediately plays, followed by the next Group, which then plays the remaining Music Segments in order. You could have achieved the same result by leaving the segments in a single Group, but what you now have is the flexibility to add behaviors to how that second Group plays.

Change the second Group to Random Step.

Step modes play only a single object in the Group, so in this case one object will be randomly selected. After that Music Segment is played, the entire process repeats because of the Infinite Loop Count setting on the first Group.