Some songs are greyed out in iTunes and won't play
My iTunes is a combination of songs I've ripped from CDs I own, and songs purchased from iTunes.
I noticed that some of them are greyed out in iTunes. I cannot check them or play them.
Suggestions?
MacBook Pro with Retina display, macOS High Sierra (10.13.2), 512 Gb SSD, 16 mg ram, mid 2015 15;