Two chords:
The first chord is tonic. The second chord is from within the key.
Try to define the chords being played in the exercise, using chord notes or scale improvising.
Optional root: C / Am or G / Em or F / Dm or D / Bm.
The score shows the key, the tonic, and the optional second chord being played.
See the answer in the bottom of the page
C instrument (demo)
Instructions
Chord-progressions
Improvise using chord-tones or scales.
The first chord is the Tonic (from the root-note of the key) You shall define the other chord.
Define the root notes, using scale or chord tones.
English (UK) 
Dansk