Answer:
It emphasizes that those underlined words are key to understanding something, or to highlight something of importance.
Explanation:
In many texts they underline keywords and stuff
Metaphor:<span>a figure of speech in which a word or phrase is applied to an object or action to which it is not literally applicable.
simile-compares two things using like or as.
onomatopoeia-</span><span>the formation of a word from a sound associated with what is named
</span>personification-<span>the attribution of a personal nature or human characteristics to something nonhuman, or the representation of an abstract quality in human form.</span>