This exercise and its variations should be played in all keys.Triads built on the first, fourth and fifth steps of a major key are major; triads built on the second, third and sixth steps are minor; the triad built on the seventh step is diminished.In harmonic minor keys, triads built on the first and fourth steps are minor; triads built on the second and seventh steps are diminished; the triad built on the third step is augmented; the triads built on the fifth and sixth steps are major.