Descartes concluded that the world must exist

A) before he proved that God existed.
B) before he proved that he existed.
C) after he first proved that God existed
D) because, from the start, it could not be doubted

Descartes' philosophical method involved doubting everything that could possibly be doubted, until he arrived at something indubitable. He first established his own existence with the cogito argument ("I think, therefore I am") and then moved on to prove the existence of God. Only after proving God's existence, who is not a deceiver, did he conclude that the external world exists.