I’ve been getting lots of emails about the “Join CD Tracks” option in iTunes 12. If you insert a CD in your drive, then select it in iTunes, there is an Options menu near the top-right of the window. Select the tracks you want to join, then click that menu and choose Join CD Tracks.
Click the Import button, and iTunes will join the selected tracks.
Note that the Join CD Tracks menu item will not display if the CD is not sorted in track order. To make sure that it is, check that there’s a ^ in the column header above the track numbers.
If not, click that header, and make sure that the track numbers are listed in increasing order (track 1 at the top).