The Logic: The "Unexpected" Contrast
The sentence sets up a situation where the tone of a new biography is a surprise based on the history of both the author and the subject.
- The Subject/Author's Preference: Both have traditionally valued "levity over solemnity."
- Levity: Humor or frivolity, especially the treatment of a serious matter with humor.
- Solemnity: Seriousness, gravity, or dignity.
- The Pivot: The word "unexpected" tells us that this new biography does not have a tone of levity. Instead, it must have a tone of solemnity, sadness, or extreme seriousness.
- The Goal: We need two synonyms that describe a sad, mournful, or gloomy tone.

The Correct Answers:
A. lugubrious
F. melancholy
- Why they work:
- Lugubrious means looking or sounding sad and dismal (often exaggeratedly so).
- Melancholy means a feeling of pensive sadness, typically with no obvious cause.
- Both words provide the "solemn" contrast to the "levity" the audience was expecting. If the author usually writes funny books, a lugubrious or melancholy one would indeed be "entirely unexpected."

Why the others fail:
- B. jaunty and C. jocose: These are "opposite traps." They mean cheerful/self-confident and playful/humorous. If the book were jaunty or jocose, it would align with "levity" and therefore would not be unexpected.
- D. frivolous: This means not having any serious purpose or value. This is a synonym for levity, so it doesn't fit the "unexpected" criteria.
- E. ironic: While a tone can be ironic, "ironic" does not have a synonym partner in this list that creates the same meaning (e.g., "sarcastic"). Furthermore, irony doesn't necessarilcontrast with levity.

Final Completed Sentence
The lugubrious / melancholy tone of the biography is entirely unexpected since both the biographer in her previous works and her subject in all that he has written have valued levity over solemnity.