Composer a short selection for mixed choir without accompaniment.
Use a wedge form in terms of dynamics (start very softly, gradually get louder).
Avoid creating a sense of pitch center. You may only use major triads (extendable to the 7th). Exploit inversions to achieve satisfying voice leading and tonal color.
Be very liberal with meter changes–obscure a sense of rhythmic regularity.
For the text, select either a Psalm or an ancient Greek epitaph.