Apple Final Cut Pro 7 - Manual (Page 447)

Since the audio and video items of each edited clip are linked, selecting the video clip
item also selects the audio clip items, and edits you make to one are automatically made
to the others. For example, if you move a video clip item from track V1 to track V2, the
audio clip items move from tracks A1 and A2 to tracks A3 and A4.
Video clip item in V1
Audio clip items in A1
and A2
...the audio clip items
move as well because
they are linked.
When you move a video
clip item to a new track...
The video clip item is
now in V2.
Linked audio clip items
are in A3 and A4.
Video and audio clip items can be linked or unlinked at any time. For more information,
see
“Linking and Editing Video and Audio in Sync.”
447 Chapter 31 The Fundamentals of Adding Clips to a Sequence