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