The researchers’ conclusion concerning the absence of demographic bias would be most seriously undermined if it were found that (A) the older an individual carnivore is, the more likely it is to have a large number of tooth fractures
这个就是作者conclusion的前提假设:因为年纪越大的食肉动物越有可能有大量的牙齿磨损,所以才有作者的结论——demographic bias will only occur if the old are overrepresented。这样明白了吗?