Which of the following is not a parasitic adaptation in general?

Pathogens have to adapt to life within the environment of the host. For example, the pathogens that enter the gut must know a way of surviving in the stomach at low pH and resisting the various digestive enzymes. 

Most parasites do not have a well-developed digestive system. For example, Cestodes lack the mouth and intestine that is present in other platyhelminths. All nutrition is obtained by absorption of molecules, principally carbohydrates, across their body surface, the tegument.