Final answer:
Amongst the given options, the theme of Sandburg's poem 'Grass' is Option A: war. Sandburg uses the metaphor of grass to represent the forgotten casualties of war.
Step-by-step explanation:
The theme of Sandburg's poem 'Grass' is A. war.
In the poem, Sandburg uses the metaphor of grass to represent the forgotten casualties of war. He depicts the grass as a silent witness to the horrors of war and emphasizes the theme of remembrance and forgetfulness. The poem conveys the idea that while war may be forgotten by society, the grass always remembers.