Which of the following correctly describes the effect parasites have on their host's population size and on the host itself?

A) Parasites have a density- dependent effect, but they do not affect host death rates.
B) Parasites have a density- dependent effect, and they usually kill their hosts.
C) Parasites have a density- independent effect, and they usually kill their hosts.
D) Parasites have a density- independent effect, but they do not usually kill their hosts.
E) Parasites have a density- dependent effect, but they do not usually kill their hosts.