Explanation

The sentence establishes a contrast: the "popular caricature" of conductors is that of "an imperious tyrant" - someone domineering, authoritarian, and commanding. Yet audiences were "visibly taken aback" by Maestro Chen's demeanor, which must therefore be the opposite of imperious and tyrannical. The blank must mean modest, not arrogant, not authoritarian, or humble.
- A. mercurial - Volatile, unpredictable, subject to sudden mood changes. Describes emotional instability, not the absence of authoritarianism. A mercurial conductor could still be imperious. Incorrect.
- B. unassuming - Modest, not arrogant or presumptuous, lacking pretension. "Markedly unassuming rehearsal demeanor" perfectly captures the surprising contrast with "imperious tyrant." Correct.
- C. dogmatic - Rigidly asserting opinions as incontrovertible truths. This is aligned with the imperious stereotype, not opposed to it. Incorrect.
- D. charismatic - Compellingly charming, magnetic. Describes personal appeal, not the presence or absence of authoritarianism. A charismatic leader can still be imperious. Incorrect.
- E. sycophantic - Fawning, servile, excessively flattering toward those in power. Describes behavior toward superiors, not the conductor's demeanor toward the orchestra. Incorrect.