What is one theme found in walt whitman's "i hear america singing"?

The themes of Walt Whitman's "I Hear America Singing" are taking joy in one's work and being productive. Whitman describes the work of people in many different occupations. He identifies some of their tasks. For example, the carpenter measures wood as he works and the girl washes and sews.

One theme found in Walt Whitman's "I Hear America Singing" is that diverse people contribute to the country's identity.

I hear America singing, the varied carols I hear,  

Those of mechanics, each one singing his as it should be blithe and strong,  

The carpenter singing his as he measures his plank or beam,  

The mason singing his as he makes ready for work, or leaves off work,  

The boatman singing what belongs to him in his boat, the deckhand singing on the steamboat deck,  

The shoemaker singing as he sits on his bench, the hatter singing as he stands,

The wood-cutter's song, the ploughboy's on his way in the morning, or at noon intermission or at sundown,  

The delicious singing of the mother, or of the young wife at work, or of the girl sewing or washing,  

Each singing what belongs to him or her and to none else,

The day what belongs to the day—at night the party of young fellows, robust, friendly,  

Singing with open mouths their strong melodious songs.  

The American poet Walt Whitman published his poem I Hear America Singing in poetic collection titled ‘Leaves of Grass’ in 1860, together with Emily Dickinson established the foundations of modern American poetry, championing masses in his works.

line a --> main

line b --> young

line c --> atitude

i also think it is d (sorry if it's not)