Read this excerpt from “o captain! my captain! ” by walt whitman. what is the rhyme scheme?

o captain! my captain! our fearful trip is done,
the ship has weather'd every rack, the prize we sought is won,
the port is near, the bells i hear, the people all exulting,
while follow eyes the steady keel, the vessel grim and daring;
but o heart! heart! heart!
o the bleeding drops of red,
where on the deck my captain lies,
fallen cold and dead.

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