Umberto Eco, an Italian author and philosopher, is known for his significant contributions to literature. He has written numerous novels throughout his career, and the correct answer is option 'D', which states that he has written 5 novels.

Below is a detailed explanation of Umberto Eco's novels:

1. The Name of the Rose:
Published in 1980, "The Name of the Rose" is Umberto Eco's most famous novel. It is a historical mystery set in an Italian monastery in the 14th century. The story revolves around a Franciscan friar who investigates a series of mysterious deaths in the monastery.

2. Foucault's Pendulum:
Released in 1988, "Foucault's Pendulum" is a complex and intellectual novel that explores various conspiracy theories. It follows the journey of three editors who create a fictional conspiracy theory that eventually spirals out of control.

3. The Island of the Day Before:
Published in 1994, "The Island of the Day Before" is a philosophical and historical novel. It tells the story of a 17th-century Italian nobleman who becomes stranded on an island just outside the international date line.

4. Baudolino:
Released in 2000, "Baudolino" is a historical novel set in the 12th century. It follows the adventures of Baudolino, a young man who becomes involved in various historical events and encounters famous figures such as Frederick Barbarossa.

5. The Prague Cemetery:
Published in 2010, "The Prague Cemetery" is a dark and satirical novel that explores themes of conspiracy, forgery, and anti-Semitism. It follows the story of Simone Simonini, a forger who becomes involved in various historical events leading up to the creation of The Protocols of the Elders of Zion.

In conclusion, Umberto Eco has written a total of 5 novels, each showcasing his unique style and intellectual depth. These novels have garnered critical acclaim and have solidified Eco's position as one of the most influential writers of his time.