The central idea of this poem centers around the death of a hero. Which line from the poem best illustrates this central idea?

a. “O Captain! My Captain! Our fearful trip is done”
b. “For you they call, the swaying mass, their eager faces turning”
c. “The ship is anchor’d safe and sound, its voyage closed and done”
d. “I, with mournful tread,/Walk the deck my Captain lies, Fallen cold and dead”