"Before I begin to describe this great city and the others already mentioned, it may be well for the better understanding of the subject to say something of the configuration of Mexico, in which they are situated, it being the principal seat of Montezuma's power. This Province is in the form of a circle, surrounded on all sides by lofty and rugged mountains; its level surface comprises an area of about seventy leagues in circumference, including two lakes, that overspread nearly the whole valley, being navigated by boats more than fifty leagues round..."

-Second letter from Hernán Cortés to King Charles V, 1520.

Why did Hernán Cortés describe the land of Mexico in his letter to King Charles?

A.
King Charles was very interested in the geography of the land.
B.
The king sponsored his journey to explore the New World.
C.
It was custom to describe the land in each letter.
D.
Cortés had to write a description due to Spanish law.