What is the branch of linguistics that studies word structure?

Excerpted from "the children's hour" by henry wadsworth longfellow a whisper, and then a silence: yet i know by their merry eyes they are plotting and planning together to take me by surprise. a sudden rush from the stairway, a sudden raid from the hall! by three doors left unguarded they enter my castle wall! look carefully at the lines above. a poem with this particular rhyme scheme is best read a. line by line. b. with long pauses. c. phrase by phrase. d. with a strong rhythm.