Question

Ah, dear father, graybeard, lonely old courage-teacher, what America did you have when Charon quit poling his ferry and you got out on a smoking bank and stood watching the boat disappear on the black waters of Lethe?

At the end of his poem, Ginsberg uses these allusions to convey a feeling of
hopefulness that modern-day America can turn back the hands of time.
doom and gloom caused by the pressure of conforming with the middle-class American society.
sadness since the speaker will never experience the same America as in Whitman’s day.
pride and appreciation for his fellow poet’s role in American literary history.

Answer 1

sadness since the speaker will never experience the same America as in Whitman’s day

The stanza is complex and a bit tough to interpret. Here's what it means in layman's terms:
"Oh, wise old Whitman, what was America like when you died, finishing your journey to the Underworld and having a rest in the afterlife?"

He's basically, throughout the poem, juxtaposing modern American society with not only the America of Whitman's day, but Whitman's beliefs regarding the direction that the country should go in. Whitman was a transcendentalist, which is about as anti-supermarket as it gets. 

Answer 2

C. sadness since the speaker will never experience the same America as in Whitman’s day.