These 4 chord progressions are all in the key of E minor.
The two bar repeating exercises only have 2 easy chords, and the rhythm is the same for each bar, so although we are working on rhythm and changing chords at the same time, these exercises are very accessible to beginner guitarists.
The chords have been simplified as much as possible, so instead of the standard G, C and D chords, they have been replaced with G6, Cmaj7, and Dsus2. These are all easier on ukulele and guitar, apart from the C chord on the ukulele, which is exactly the same amount of easy! Furthermore, these simplified chords still sound great, and do sound ok when played with the standard chords, so these could be used for other exercises or in songs, when struggling to play G or C for example.