By highlighting absence in these lines from a poem, which technique is used to add emotional intensity?

o captain! my captain! rise up and hear the bells!
rise up! for you the flag is flung, for you the bugle trills:
for you bouquets and ribboned wreaths; for you the shores a-crowding:
for you they call, the swaying mass, their eager faces turning.

o captain! dear father!
this arm i push beneath you.
it is some dream that on the deck
you've fallen cold and dead!
(from "oh captain! my captain" by walt whitman)

choices

repetition
assonance
personification
simile