单项选择题

The author's discussion of Emerson, Thoreau, Hawthorne, Melville and Whitman is primarily concerned with explaining ______.

A.some of their beliefs concerning the world and the place that humanity occupies in the universal order
B.some of their beliefs concerning the relationship between humanism and democracy
C.the way some of their beliefs are shaped by differences in temperament and literary outlook
D.the effects of some of their beliefs on their writings