Answer:
The lines that best expresses the theme of the poem are:
A) "Oh, nefarious war! I see why arms /
Were so seldom used by the benign sovereigns."
Explanation:
The poem "Nefarious War" describes the horrors of the Chinese battles against the Tartars and criticizes the fact that war accomplishes nothing.
The lands of China are covered with corpses of fallen soldiers, their insides being eaten by birds, their horses crying woefully. After this awful description, the speaker states:
So, men are scattered and smeared over the desert grass,
And the generals have accomplished nothing.
Oh, nefarious war! I see why arms
Were so seldom used by the benign sovereigns.
The poem is criticizing the uselessness of war. Its brutality brings nothing but pain and suffering. Benign sovereigns can see and understand that, which leads them to avoid engaging in war. Since they truly want their people to be happy, they do not send them to meaningless fights. Sovereigns who do not avoid war at all costs end up facing other costs - their people's lives and happiness.