Which of the following, if true, would cast the most doubt on the author's contention regarding Chopin the pianist? A. Chopin rarely, if ever, played the piano works of other composers. B. Apart from a cello concerto and a few other works, Chopin composed mainly for the piano. C. Chopin seldom performed his etudes in concerts, preferring to play in front of a small group. D. Not all of Chopin's compositions are as difficult to execute as his etudes. E. Chopin himself acknowledged that he was primarily a composer, and would have composed even more difficult pieces had he the ability to play them.