Question: The Battle of the Labyrinth is the fourth novel in a pentalogy of adventure and mythological fiction books that have sold more than 45 million copies, and have been sold in how many countries?
Sentence (from "The Battle of the Labyrinth"): The Battle of the Labyrinth is a 2008 fantasy-adventure novel based on Greek mythology; it is the fourth novel in the "Percy Jackson & the Olympians" series by Rick Riordan.
Relevant evidence: Yes