What could it be that “throbs with both fists and knows only what Salvador knows”?

- "the die is cast; i have consented to return if we are not destroyed. thus are my hopes blasted by cowardice and indecision; i come back ignorant and disappointed. it requires more philosophy than i possess to bear this injustice with patience. i have lost my hopes of utility and glory; i have lost my friend."

answer: do

the 'italicized phrase' is a noun clause that is used as a direct object.

the answer is "a" although apex might say best book of the year.