For your question, the answer would be; "C. The heroism of unquestioning sacrifice". This is because the poem tells the story of a brigade consisting of 600 soldiers who rode on horseback into the “valley of death” for half a league. They were obeying a command to charge the enemy forces that had been seizing their guns.
Could you copy and paste the lines, I don’t know the poem, but I’m great at inferences
Most likely subject not sure though