繊細

彼女は ___ な手つきでピアノを奏でた。

The correct answer is 「繊細」(せんさい), meaning "delicate," "subtle," or "sensitive." Playing the piano with 繊細な手つき (delicate/subtle touch) suggests a skillful and nuanced performance, where each note is played with precision and feeling. 「大胆」(だいたん) means "bold" or "daring"; a bold touch might imply strong, forceful playing, but not necessarily nuanced or precise. 「粗末」(そまつ) means "coarse," "crude," or "poor quality"; a crude touch would suggest clumsy playing, which is negative. 「軽快」(けいかい) means "light" or "rhythmical"; while a light touch can be part of piano playing, 「繊細」 captures the nuance and precision more broadly, fitting a skilled performance.

正解は「繊細（せんさい）」です。「繊細な手つき」は、細やかで丁寧、感受性の高い、微妙なニュアンスを表現するような演奏を指し、ピアノの演奏に最もふさわしいです。「大胆」は思い切りが良いこと、「粗末」は粗いこと、「軽快」は軽やかでリズム感があることで、文脈に合いません。