In the context of Cmi7 (dorian) layering a D major triad can add a useful tension. The basis of the exercise is to insert the D triad into a melody. The initial line is built on Cmi7 with a 4th included. With the D triad you gain a 2nd and #4. The triad advances one note each time it is inserted revealing a different phrasing with some being more useful than others. Ultimately the goal is have a free use of the technique. The last two lines are more freely composed.
