This is the first time I've understood diatonic chords, how a key called C Major could have a chord called D Minor. (I am not much of a musician nor a serious

This is the first time I've understood diatonic chords, how a key called C Major could have a chord called D Minor. (I am not much of a musician nor a serious student of music theory. If I were, I guess I would have eventually learned diatonic chords some other way. But it just goes to show you how good this course is, that a person with a passing interest in music theory was able to quickly learn even that.)