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.
A. ababcced
B.
ababcdde
C. aabbcded
D.
aabbddee