How do the images of travel in part 46 of "song of myself" contribute to the poem’s theme?

a.) they suggest that human life is impermanent.
b.) they show that growth involves a steady movement forward.
c.) they remind readers that the poem is about journeying within one’s self.
d.) they suggest expansiveness, or extending one’s reach outward.

D. They suggest expansiveness, or extending one's reach outward.

Throughout part 46, Whitman explains that a person's journey is his own, but it must extend beyond what the person currently knows. He compares needing to extend oneself to kicking them out of the comfort or their house or sending them off the plank into the water to swim. He introduces this idea of extending one's reach when he says "we but level that lift to pass and continue beyond."