Putting two north poles or two south poles of two magnets together makes
the magnets push each other apart.
Putting a north pole with a south pole
makes the magnets stick together.
For which of the following could the
magnets serve as a simple model?
A. parallel circuit
B. voltage
C. law of electric charges
D. potential difference

answer is a

explanation:

parasites can detrimentally affect their host, but also must not allow their host to die before they can complete their life cycle. some parasites have complex life cycles with many different hosts, and have had to find ways of persisting in many different environments during the change from one host to another. ectoparasites live outside the body of the host, and can more easily  disperse, but are  more exposed to predators, parasites, parasitoids. endoparasites live inside the body of the host, and are therefore protected from the outside environment. but they can be  attacked by the host's immune system. they have therefore developed  mechanisms for dispersal such as  complex life cycles.