20 of 20: In this photo taken April 18, 2012, provided April 19 by the Chicago Zoological Society, a Mexican gray wolf is seen at Brookfield Zoo?s Great Bear Wilderness exhibit in Brookfield, Ill. Through a study of Mexican gray wolves, researchers hope to aid in conservation efforts of the endangered species, and determine whether a type of nasal tumor is more prevalent in wolves or domestic dogs. The Chicago Zoological Society, which manages Brookfield Zoo, is embarking on a study to determine the occurrence of nasal carcinoma in Mexican gray wolves using CT (CAT) scans. (AP Photo/Chicago Zoological Society, Jim Schulz) (AP Photo/ Jim Schulz)

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