Which of the Following Characteristics of Parasites Explains How Parasitism

Which of the following characteristics of parasites explains how parasitism has become so widespread among living organisms?

A) Parasites almost always predigest their hosts' tissues and, therefore, spend less energy and require fewer structural adaptations.
B) Parasites, unlike predators, feed on almost all the tissues of their host.
C) Parasites do not generally kill their hosts; thus they can feed on the same host throughout the host's normal life span and do not have competition from decomposers.
D) Parasites generally kill their host and can feed for a very long time because they are much smaller than their host.