The CD (Single) must contain the featured track or a version/remix of it.
The CD (Single) must meet the minimum dealer price requirement.
The CD (Single) must have no more than 4 different tracks, although each song may appear in any number of different versions.
The CD (Single) maximum running time is 25 minutes (if more than one different song is featured), or 40 minutes (if one song is featured in multiple versions/mixes).

So the important bits that make a CD qualify as a CD Single.
No more than 4 different tracks (not counting any remixes of the same song).
No more than 25 minutes in playing time (for up to 4 different tracks) or up to 40 minutes if the CD contains remix versions.