Which figurative language device is exemplified by "the presentation of a thing with underemphasis"?

The correct answer is B, meiosis, which refers to a rhetorical device that deliberately understates or downplays the significance of something. This technique is often used for irony or to create a subtle, humorous effect. For instance, if someone were to refer to a significant injury as "just a scratch," they would be employing meiosis to minimize the importance of the injury.

In contrast, the other options do not fit this definition. A metaphor involves a direct comparison between two unlike things, often to highlight similarities. Alliteration focuses on the repetition of consonant sounds at the beginning of words in close proximity, which serves a different stylistic purpose. An idiom is a phrase that has a figurative meaning not deducible from the literal meanings of its individual words, which also does not align with the concept of underemphasis. Therefore, meiosis is the only term that accurately captures the essence of using understatements in expression.