Which statement best describes the theme of this stanza?

the tide rises, the tide falls,
the twilight darkens, the curlew calls;
along the sea-sands damp and brown
the traveller hastens toward the town,
and the tide rises, the tide falls.

a; nature and humans move independently of each other.
b; human beings are challenged by events in the natural world.
c; human beings have built too many towns near natural resources.
d; nature will eventually solve all of humanity’s problems.