Answer: (D) Alliteration
Alliteration occurs when words in the text have similar initial consonant sounds. Three words in sequence begin with the /n/ sound, "nodded, nearly napping" and "nodded, nearly napping". The alliteration links the three words by their first sound. Nasal consonant /n/ is a smooth, soft sound. To make the /n/ sound, air is stopped from coming out of the mouth because of where the tongue is placed and is forced to come out of the nose. Interestingly, this sound is the same sound that someone might make inadvertently while sleeping--a deep breathing sound that is not quite a snore. So using the repeated /n/ sound to describe someone who is about to fall asleep helps the reader experience that state simply through the sounds of the words. In addition, the fact that the three words have identical rhythm--a stressed syllable followed by an unstressed syllable--reinforces the effect. One can almost feel the sensation of the man's head starting to droop and the man catching it with each new stressed /n/ syllable. The use of alliteration and rhythm in this way helps the reader enter into the mood and action of the poem.