Before and during the Civil War,（ ）stood firmly on the side of the North and wrote a series of poems gathered as a collection under the title of Drum Taps.

• A、Walt Whitman
• B、Nathaniel Hawthorne
• C、Herman Melville
• D、Mark Twain

Best of all the well-known lyric pieces is（ ）by Percy Bysshe Shelley.

• A、Ode to Liberty
• B、Men of England
• C、Ode to Naples
• D、Ode 10 the West Wind

Briefly discuss the theme of Walt Whitman's volume of poems Leaves of Grass.