Answer: A. Abraham Lincoln has tragically died.
Explanation: In the poem "O Captain! My Captain!" by Walt Whitman, the speaker is referring to Abraham Lincoln who has tragically died. The speaker both celebrates that the ship has arrived safely and mourns the death of its leader. This poem is an extended metaphor, in which the Captain represents the President's Lincoln death, and the safe arrival is the end of the Civil War. It is a poem of both loss and celebration.