Which Statement About Density-Independent Factors Is True

Which statement about density-independent factors is true?

A) Davidson and Andrewartha's studies of thrips (Thrips imaginis) showed that density-independent factors play a major role in the annual fluctuations of abundance of this species.
B) Density-independent factors increase the size of populations when population size is low.
C) Density-independent factors decrease the size of populations when population size is high.
D) Food and habitat availability are density-independent factors that influence population size.