Answer
The three iconic composers, Haydn, Mozart, and Beethoven, all had the privilege of studying C.P.E. Bach's influential treatise titled "Essay on the True Art of Playing Keyboard Instruments." This seminal work, published in 1753, offered invaluable insights into performance practices, ornamentation, and expressive techniques specific to keyboard instruments. Their exposure to Bach's expertise profoundly shaped their musical development and left an indelible mark on the trajectory of classical music.