D. Castiglione
Cesare Borgia was the Son of the Pope and Cosimo de Medici's family ruled Florence, so neither have anything to do with the royal family of Mantua. Machiavelli wrote the Prince, so that is not the correct answer either. Castiglione was part of the Royal family of Mantua and did write the Book of the Courtier. So D is the correct answer.
B) Kelper: planetary orbits
Kelper had a similar theory of Copernicus
The answer I believe would be B
