Read this and answer the question. If the question is unanswerable, say "unanswerable".

The earliest surviving written work on the subject of architecture is De architectura, by the Roman architect Vitruvius in the early 1st century AD. According to Vitruvius, a good building should satisfy the three principles of firmitas, utilitas, venustas, commonly known by the original translation – firmness, commodity and delight. An equivalent in modern English would be:

What are the three principles every plan should consider?
firmness, commodity and delight.