premise: A tour group plans to visit exactly five archaeological sites. Each site was discovered by exactly one of the following archaeologists—Ferrara, Gallagher, Oliphant—and each dates from the eighth, ninth, or tenth century (A.D.). The tour must satisfy the following conditions: The site visited second dates from the ninth century. Neither the site visited fourth nor the site visited fifth was discovered by Oliphant. Exactly one of the sites was discovered by Gallagher, and it dates from the tenth century. If a site dates from the eighth century, it was discovered by Oliphant. The site visited third dates from a more recent century than does either the site visited first or that visited fourth. The tour group could visit at most how many sites that were discovered by Ferrara?
hypothesis: four